Protecting over 200 million PCs, Macs, & Mobiles – more than any other antivirus

December 4th, 2009

Apologies for Bad Definition Update

You may have heard that we released a virus database update early Thursday morning (or Wednesday night depending on the time zone). We are deeply sorry for releasing this update and the trouble it caused you. Of the users that received the update, most encountered no problems, some encountered minor issues, and some had significant problems.

I apologize to each and every one of you—I realize that security is fundamentally about trust and you have to trust your security provider. We made a mistake here and it won’t happen again.

We have highly automated systems and processes for testing and releasing virus updates. Updates are thoroughly tested before being released. But the process failed due to a “human failure”. This was an example of the old proverb “the road to hell is paved with good intentions”. Some engineers thought they were doing the right thing by sending out an out-of-cycle update to fix a problem. Unfortunately, they circumvented the automated systems and ended up sending out the wrong update—one that had not yet been tested.

There are detailed explanations of this issue and how to fix it on our support forum ( And our CTO has authored a detailed explanation of how this happened ( In the next few days I will write another blog entry about how we are changing our processes to ensure this problem does not ever occur again.

In the meanwhile, please accept mine (and the company’s) apologies for the troubles we have caused you. We won’t let it ever happen again.

Categories: CEO's corner Tags:
  1. Cindy
    December 4th, 2009 at 19:06 | #1

    Thanks for letting us know the mistake and the immediate course of action you took. Makes me love this product even more. I have been using at all my client locations and despite the troubleshooting I did yesterday getting programs working again – totally trust your product. Thanks for the notification of the problem.

  2. December 4th, 2009 at 19:57 | #2

    No problem Avast. Avast is best anti virus product on the world. :)

  3. December 4th, 2009 at 20:02 | #3

    Those things happen sometimes. I am very impressed by how quickly you caught it and fix the issue. Glad to hear you are taking steps to make sure that kind of thing doesn’t happen again.

    In the meantime, keep making great software!

  4. December 4th, 2009 at 20:21 | #4

    Stuff happens. Avast is still the best.

  5. December 4th, 2009 at 20:45 | #5

    I agree. It can happen to anyone. In fact it did to pretty much all major vendors like Kaspersky, McAfee, Symantec and Trend Micro. They all encountered such problem, some even more than once. But this doesn’t change the fact that avast! free is application that’s hard to match even by commercial versions that cost lots of money.
    ALWIL team admitted, explained, helped correct this and apologized. I think it was perfectly fair from their end.

  6. John
    December 4th, 2009 at 20:50 | #6

    I had 72 files on my office system falsely tagged. I had Outlook unload DLLs and force me through unregistering the apps. I believe I now need to reinstall these products to reactivate. I have this on my Windows Home Server device and am sure I have additional cleanup to perform.

    This had a major impact to my setup. Thank you for taking additional actions. Interesting the the applications effected provided me warnings/updates, however I had to read about your error and then launch the Avast program and go to the Virus Chest to understand what happened.

    A) when such a large amount (in comparison to normal operations) of files are identified, can’t you notify (e.g. email, popup, etc.) the user that something is amiss

    b) are there settings that provide this level of notification

    I understand, but am still annoyed…. Thanks for the quick response though.

  7. Susan W.
    December 4th, 2009 at 21:02 | #7

    Thank you so much, my daughter and I were both having problems, different households. at least I only uninstalled ad-aware, before I realized that it had to be with avast. Humans make mistakes. at least I know I can go back to Avast! I uninstalled it and was tryiing out a new one. I use to pay for. I Now can go back to avast.
    again thanks

  8. jkargan
    December 4th, 2009 at 21:12 | #8

    This matter has caused me a major problem, part of it my own fault. It read one important file in my Acronis True Image backup as a virus. Since I have learned to trust Avast AV a bit too much, I deleted the “virus” file without reading the warning too carefully. I lost my incrementally saved backup images of my C: drive. I now have to wipe my C: and install Windows XP all over again. After that, I have to reinstall my myriad of programs. I have to do this because my first incremental backup with Acronis is of my C: drive with only Windows on it. This is my fallback position in case of some catastrophic crash of Windows.

    Yes, I know you have apologized, bu I just want to point out what your negligence has cost some of us. Unfortunately, you caught me napping and I increased the problem with my own actions.

  9. December 4th, 2009 at 21:48 | #9

    This affected my brother’s Home PC as he was getting a Trojan Horse alert when he tried to use Auslogics Disk Defrag. I told him it was a False Positive and to just update Avast and it would be fixed. He did that today and everything is good.

    I give you high marks for admitting your mistake and taking steps to correct it and improve the process. It shows me that you are truly a customer focused company.

    Keep up the good work!

  10. Mikael S Hedman
    December 4th, 2009 at 21:59 | #10

    I´m not at all happy about “… how quickly you caught it and fix the issue …”, because my computer won´t boot although I followed all your recommendations … I restored `infected files´ from virus chest (but 19 files couldn´t be restored … the original location wasn´t to be found … i saved this report but I can´t read it …), updated to 091203-1, checked that one of the `infected programs´ (IObit 360) could run again. Then – before making a reboot – I made a registry fix with `IObit Advanced SystemCare v3.4.1´ (a program I´ve used alongside Avast Free for about one year without any problem.

    Now my computer (with genuine Windows XP, fully updated) won´t boot … in fact I can´t access BIOS set up and – what´s even worse – it doesn´t respond to my wired mouse or any key on my wired keyboard (I think some of the files that couldn´t be restored from virus chest said something about “key” or “keyboard”) …! My last atempt was to disconecct the power and remove the back up battery for about one hour, but the computer won´t boot … I´ve even tryed to boot with both the Windows CD and the ASUS CD that came with the motherboard … I´t seems that my BIOS is permanatly damaged … can you please help me; your appologuise and your recommendation isn´t enough for me!!

    /Micke (from Sweden)

  11. December 4th, 2009 at 22:06 | #11

    Thank you for the update, the mistake had hit my system prety hard but luckily thanks to the commuity and your team, things were resolved quickly with little damage.

  12. reijo blomberg
    December 4th, 2009 at 22:07 | #12

    Yes, I have this problem. Avast delete my Mail washer program and skype program also and tell me I have trojan my computer (new windows 7 this computer) I must go avast net scanning, but Idont this program. I think I have new f secure box my home. I install fsecure virus scan, and this program delete Avast professional virus scan. I have 1 year licence f secure program, I send email firetrust, and they send my email, that error (fake) is Avast program and Avast make new version this daily send virus basic

  13. zen
    December 4th, 2009 at 22:27 | #13

    Poor show

  14. ALEX
    December 4th, 2009 at 23:02 | #14

    Didn’t know was a false alarm. Tried to use AVAST! to correct the problem. Ended up screwing my machine so badly I needed to reformat my drive and reinstall windows from scratch. It’s great you advance an apology and everything but the fact remains my machine was damaged beyond recovery and I lost a lot of irreplaceable files.

    Now all you flamers can jump my butt and tell me I don’t know how to use a computer and damn me for being critical of your pet software. Fact is, I don’t care. My machine was totally screwed due to a MAJOR screw-uo on the part of AVAST! and I won’t apologize for being unhappy about that. So you fan-boys can go climb a rope.

    So goodbye AVAST! and I’ll find a GOOD anti-virus program (and no, I’ll not let the door hit me on the way out). :-)

  15. Elle
    December 4th, 2009 at 23:35 | #15

    I’m sticking with Avast!; even with this, it’s still better than the alternative.

    The update did screw up my computer because at the next start-up, it would freeze before it would load the sign in screen. I’m not very computer savvy, but I was able to get my computer back up and running. At first, when it froze and I restarted it, I could get into safe mode but repairing from inside safe mode did not work (I tried different times to boot from, but none of them worked).

    So, I tried something else. The second Vista started, I pressed F8 and “start repair” on that screen, which got it back to normal.

    Mistakes happen and at least you guys are owning up to it. Thanks for making a quality anti-virus.

  16. Dennis
    December 4th, 2009 at 23:41 | #16

    I uninstalled when false positives were raining down. I was going to try another antivirus program. I read this and changed my mind. I’m going back to Avast.

    This error will no doubt hurt your user-base. The way you are dealing with it, however, is exemplary.

    Good show…

  17. andy booth
    December 4th, 2009 at 23:42 | #17

    Aww diddums! Is that dummy spit a ‘Personal Best’?

  18. wonder
    December 4th, 2009 at 23:53 | #18

    I can understand that many people are angry since they lost precious data etc…but…do you think other vendors are perfect/immune to these problems?? What about kaspersky? Due to a bad update they killed a lot of computers deleting explorer.exe!!! It happened. What about avg?? same problem last year..a lot of innocent files deleted…so you guys can change AV…till the new security provider then?? Will you change again and again??
    I’m sorry to hear persons saing they are using avast from many years..and now, due to a SINGLE human error, they are ready to spit on the dish they eated and appreciated for a long time.
    No, I don’t like this behaviour.

  19. Joe Wallner
    December 5th, 2009 at 00:05 | #19

    Got the trojan horse warning at 9:30pm Wednesday night-rebooting & scanning ran into a series of error messages after only 3% was done; 8 files were reported as infected.

    Took it to my local shop for a $60 virus scan on Thursday. This is more than an “inconvenience”.


  20. alan taylor
    December 5th, 2009 at 00:22 | #20

    Thank you for all you do!!! One small glitch, in what is a tremendous service to computer users around the world can easily be forgiven..

  21. December 5th, 2009 at 01:24 | #21

    Scared **** out of me, as I am NOT as ‘techie’ as I’d like to be. Alarms went off and I moved the ‘bug file’ to the chest. Didn’t fix the problem, though, and the next thing I know, upon re-booting, I was stuffed – no go.

    A$110 later, all ok – but I had to uninstall some programs because I don’t want this happening again!

    I had a very good car once, which played up. I stuck it out and bought another in due course. So, avast, I’ll stick with you. Naivete tells me ‘these things happen’.

  22. Murad
    December 5th, 2009 at 03:06 | #22

    Your bad definition update deleted 105 files from my PC, I have more than 13 years of experience in the IT field and this is the first time i face a disaster like this caused by the software that should protect my system from viruses … sorry but i can’t trust you now and i will not use your software or recommend it to anyone.

  23. Dave
    December 5th, 2009 at 03:56 | #23

    avast! is a great program and this was the first problem. You addresses it quickly and provided a solution. Thank you for such a good program and the rapid attention to the “problem”. I will still use the program and encourage others to do the same.

    avast! to the rescue – it works!!!!

  24. Liam
    December 5th, 2009 at 04:26 | #24

    Here is my suggestion: aim for quality in a release not quantity. If that means a slower response then so be it. As a user I want quality in my AV not necessarily quantity.

    I would prefer one good release a day versus three crappy releases a day – if you know what I mean.

  25. Sandra
    December 5th, 2009 at 05:27 | #25

    I have just spent a harrowing 3+hours getting my computer back to ,I hope, normal,
    after Avast threw up an alert that my computer was infected with Win32 Delf-MZG [Trj].
    In the lengthy scan Avast would only delete, not repair, many, many files some of them exe files of programs I have been using for ages plus a lot of .dll files.
    Avast also said some Windows system files and memory were infected (can you imagine just how panic stricken I was?)
    I have just become operational again and when I googled for information on that Trojan I found that others have had the same problem with Avast giving that warning when in fact what it is picking out is what they call false positives.
    Now I am not overly computer literate or clever and although I have managed to get the ‘deleted’ programs and files up and running again I thought others here should be made aware that Avast is doing this when in fact, it appears there is no need to scare the daylight out of old ladies with these false positives warnings.

    I don’t know if other members have had this happen to them.

    Must be time for a stiff drink before I retire for the night, I think I’ve earnt that.

  26. xstyle
    December 5th, 2009 at 05:49 | #26

    Tnx Avast for fast action! User’s should read sometime’s so they know wants happening.. Avast support as for free and a single glitch everyone starts complaining??? come on guys!

  27. December 5th, 2009 at 05:50 | #27

    Hi There,

    I agreed with wonder,
    Just only once human errors, your guys which feel avast bad looks very childish.
    If everyone which disappointed with avast! and want to move to others vendor, just go ahead. But if sometimes back to avast! again, let see what you had said formerly and you pull it back to use avast!…not a very gentleman matter.

    But honestly Vince and ALWIL Team has quickly responsible and respnd to solved this problem, and have a gentleman quickly respond to acknowledge this problem.

    Just keep do the best Vince Steckler and ALWIL Team.

    Yanto Chiang

  28. xstyle
    December 5th, 2009 at 05:59 | #28

    Avast shows the detected TROJAN Virus like Spybot, Skype & etc…. We all know that we use this kind of program before it happens&suddenly this 1 strikes, So do you think you should delete it?? or maybe you should start searching & reading something about it before doing anything!ayt??

    Dont just depend, start learning guys!


  29. maduser
    December 5th, 2009 at 06:12 | #29

    Well, well,

    I just got in the face with avast = format hardrive and re-install all.

    so no more avast in this computer and heading to something else with a better control. Maybe Nod32 or avg…

    Thank you for wasting my time.

  30. December 5th, 2009 at 06:23 | #30

    maduser :
    Well, well,
    I just got in the face with avast = format hardrive and re-install all.
    so no more avast in this computer and heading to something else with a better control. Maybe Nod32 or avg…
    Thank you for wasting my time.

    Go ahead maduser,

    Let see someday are you will back to using avast?

    Then someday you will remember what had you said today.

  31. MarkAW
    December 5th, 2009 at 06:27 | #31

    Thanks for letting us know and the quick fix to this problem. Avast still is and will always be my AV of choice.

  32. Ashok
    December 5th, 2009 at 07:25 | #32

    Thanks for the big thing first..”Free and effective Antivirus”..These minor things like false alarm do happen once in a while, “To err is human” ofcourse..but main thanks for quick fixing and letting us known. I trust Avast.
    And please keep this CAPTCHA code before the “Submit content” button. i ended up in error.

  33. Ron
    December 5th, 2009 at 08:08 | #33

    Avast, you caught the problem early and you were credible enough to own up to it. That’s commendable. But if the the “human error” was caused by carelessness on the Avast staff, I hope that persons involved will be properly dealt with.

  34. December 5th, 2009 at 08:31 | #34

    Hi,avast no problem with you Still yet.But i noticed one thing,That if virus is on the system it won’t detected it automatically shutdown,And not so much secure on the system.M not using the internet but i manually download the updates.From 2 days m downloading the updates that also not coming because it having 34.49mb but copying only 34.4mb only..Plz help me out this problem…thanking u…

  35. Bart
    December 5th, 2009 at 08:46 | #35

    I really had some fun time, lol, love solving computer related problems ;) been a 3rd line help desk guy 4 years, and yes had a huge problem with Avast’s update :(
    3 of my programs were marked, Auslogic defrag, and Spyware Terminator and Iobit 360..
    my Vista would not really start again hadda do a diff thingy
    went into safe mode, removed the start up and deleted the software :(
    after that it did start, googled 4 Win32 Delf-MZG [Trj]. and found that Avast caused the problem :( …updated Avast

    well, shit happens, keeps techies up to date, lol
    I will stick with Avast, no matter what, and will also tell my friends to do so

  36. shae_32
    December 5th, 2009 at 11:22 | #36

    I have to say, that was a scary one, but fortunately, Avast caught it quickly. These type of things unfortunately, happen in the computer security world. Scary, but it does happen. I do have to second the idea that an update a day is sufficient. :) I do know that stinkers seem to mulitply by the bazillion, but I’d much rather have a quality update as opposed to several a day that could be buggy. :S Since I’m studying for a computer certification, this no doubt was a “hands on” learning experience for me. LOL I certainly hope that whoever “let the donkey out of the stable” gets a stern repriminding. ;)

  37. Jack
    December 5th, 2009 at 11:32 | #37

    I was lucky and caught this before it did major damage. I had to reinstall 2 programs Spybot Search & Destroy and Tuneup utilities. I quickly rebooted my system in safe mode and removed Avast as it made my computer freeze up. I switched to a different Anti_virus program which I will use for now. I may go back to Avast, but feel that it can’t be trusted. I still think Your site got “Hacked” and you are not willing to admit it. I know people who had all their anti-virus & Ant-Malware programs hit also all their dll files deleted and all their exe fikes.

  38. Jack
    December 5th, 2009 at 11:39 | #38

    I was lucky we have 2 computers and when first one got hit i figured it was a false positive. Then my computer got hit so I called my son who is a techie and could hear the alarms going off. While talking to him my other sons computer got hit as well. Luckily we all were smart enough to not delete or move any of the files, and removed Avast from our systems. But this is 4 users who have left wonder how many of the close to 1 million have done the same.

  39. December 5th, 2009 at 13:26 | #39

    I am glad to here the issue was not just my own. I will re-install Avast! when I am sure all problems have been cleared up. (By waiting a week or so.)

  40. Runa
    December 5th, 2009 at 15:16 | #40

    It takes a big man to acknowledge his mistake and apologise for it publically. Thank you. Well done.

  41. Adam
    December 5th, 2009 at 15:25 | #41

    At Least you don’t STEAL definitions updates like what IObit stole Malwarebyte’s definitions .
    Good luck avast

  42. Raedwulf
    December 5th, 2009 at 15:47 | #42

    See now I had no problems. I pay attention and therefore knew about the faulty update by the time it got to my comp, and didn’t install it. If any of you had damage from this its your own fault. All the anti virus programs have occasional problems, from faulty updates to the complete inability to do anything about a new virus. The point is you need to accept responsibility for yourself, the anti virus is there to help you, not guarantee smooth sailing. Of all the options out there I say avast is the best there is. I have used it for years now and on many different computers, and overall its made my life one hell of a lot simpler than other virus programs ever did.

  43. Tom.B
    December 5th, 2009 at 16:54 | #43

    I would say that I am one of the lucky guys then as I have had no problems of the sort as it relates to the botched definition update and happy that said problem was corrected before it could have affected me. I will continue to use Avast as I have always liked it’s features especially for a free product :-D

    I am however disappointed in the faithless people who have abandoned Avast because of a single human error. That’s just weak :-(


    – Tom ;-)

  44. unicorn
    December 5th, 2009 at 17:18 | #44

    This issue should have NEVER happened. This issue has impacted your commerical, public sector, users of your product. The person or person(s) responsbile for this mess should resign or be fired! Enough said?

  45. Keylth Carey
    December 5th, 2009 at 17:52 | #45

    I have been using AVAST for seven years, and one major glitch happened. I had to quarantine about 80 files, scan the HD, and reinstall 5 programs. Noetheless Avast remains the best Virus protection available in my opinion. Thank you for a great service and product, as always. Can’t wait for Avast 5

  46. December 5th, 2009 at 18:07 | #46

    `I am a loyal user of Avast and I appreciate the ethics [ honestly ]! Can you tell me if Avast will create a bootable cd with software and Avast to remove viruses?
    the apology was well written.

    A satisfied customer,
    dennis j merritt

  47. kye
    December 5th, 2009 at 18:28 | #47

    i have no problem, with Avast! your software was able to destroy a stubborn rootkit that Mcafee virus scan didn’t even detect, the team responded as quickly as they could, in what i believe was a very responsible move.
    Although i only use the software to remove extremely stubbon malware, one mistake will not affect me.

    Finally i will be using avast 5 as i already love your beta!

  48. icemel
    December 5th, 2009 at 21:36 | #48

    I agree. 1 signature file a day is more than enough.
    Same with software versions. Once a year is good enough.

  49. December 5th, 2009 at 21:58 | #49

    icemel :
    I agree. 1 signature file a day is more than enough.
    Same with software versions. Once a year is good enough.

    Its okay for me if avast not release to many definition updates when it is not emergency. The today avast is more than good enough for me. I think I will not stop using avast, since I found no others as a better alternatives :)

  50. Patrick
    December 5th, 2009 at 22:03 | #50

    Lucky me. I just installed avast on my computer Thursday without any awareness that this problem had occurred. If I’d installed it one day earlier …

Comment pages
1 2 3 720
Comments are closed.