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Consumer Products => Avast Free Antivirus / Premium Security (legacy Pro Antivirus, Internet Security, Premier) => Topic started by: twn321 on March 08, 2013, 06:17:36 AM

Title: Possible false positive?
Post by: twn321 on March 08, 2013, 06:17:36 AM
Hi there all. (New here, so forgive me any omissions or errors in the following.)

So... I ran a boot time scan yesterday. No problems/all clear. Today, for whatever reason, I ran one again. And I got the following message:

File C:\Windows\assembly\NativeImages_2.0.50727_32\stdole\f698ac346476a20a02725b8e9de422cd\stdole.ni.dll is infected by Win32:Malware-gen.

Hadn't done anything during the day that I hadn't before yesterday's scan except update Adobe AIR and 64-bit Java- both on Avast's advice- plus update to the latest version of Avast, too. And to be told, the computer was running just fine all night last night (after yesterday's scan) and today. So, am I maybe looking at a false positive here? That said... as the above item is in a Windows folder, I did not want to just blindly go ahead and do something that I might not be able to undo (if needed). Is the above item safe to delete? To move to chest? To repair? Or, can it be ignored? For the time being, I have done the last thing...

Appreciate your advice/comments.
Title: Re: Possible false positive?
Post by: twn321 on March 08, 2013, 06:20:23 AM
Oh... I almost forgot:

When I scan the Windows\assembly folder with Malwarebytes, everything comes up clear. No infection found.
Title: Re: Possible false positive?
Post by: A. User on March 08, 2013, 06:27:28 AM
If the file is NOT quarantined, you can upload it to Virus total here: https://www.virustotal.com (https://www.virustotal.com) and see the results.
Title: Re: Possible false positive?
Post by: twn321 on March 08, 2013, 06:42:33 AM
Thanks for the tip. My only problem is that when I try to do what you've suggested ("Choose File" to be scanned by VirusTotal), I am unable to find said file in the Windows\assembly folder. And I do have my preferences set to show hidden files/folders. Any additional ideas?
Title: Re: Possible false positive?
Post by: ulix79 on March 08, 2013, 07:34:47 AM
I'm having the same problem. Can't find the file. Any suggestions?
Title: Re: Possible false positive?
Post by: true indian on March 08, 2013, 07:35:55 AM
it should be in your virus chest...

UI>>Maintainence>>virus chest>>select the file>>hit extract>>extract it to desktop>>upload to www.virustotal.com
Title: Re: Possible false positive?
Post by: twn321 on March 08, 2013, 07:52:42 AM
it should be in your virus chest...

UI>>Maintainence>>virus chest>>select the file>>hit extract>>extract it to desktop>>upload to www.virustotal.com

Not if you haven't moved it to the chest. And that was part of my original question. More specifically, during the boot time scan, avast asks you if you are sure about moving a file that is in a Windows folder to the chest. Is it okay to do that?
Title: Re: Possible false positive?
Post by: ulix79 on March 08, 2013, 08:02:57 AM
Avast doesn't allow me to put it in the chest. It's not there.
Title: Re: Possible false positive?
Post by: Undead-Divine-Assassin on March 08, 2013, 02:30:22 PM
I found this Win32: Malware-gen thing on my Dell WinXP laptop last weekend during my post monthly program and Windows updates boot time scan with Avast. It wasn't there on 02/02/13 the last time I did an Avast boot time scan.

Neither earlier numerous quick scans made during the month found it and full system scans with Spybot or Malwarebytes flagged up nothing wrong post updates either.

The 'malware' was located in Windows default hidden Restore Point folder and I used the Avast delete option to kill it.

A new boot time scan was clean and I have had no problem since
Title: Re: Possible false positive?
Post by: A. User on March 08, 2013, 04:53:33 PM
Well, you can search the file by entering its name in the search box when you open "My Computer". Are you sure you checked the virus chest and the "stdole" directory? I'm not a virus removal expert, but if you think you are infected you can scan your computer with some of the tools here: http://www.selectrealsecurity.com/malware-removal-guide (http://www.selectrealsecurity.com/malware-removal-guide) or you can post a new topic in the "viruses and worms" section, where you will get further assistance. Open avast GUI> security> antivirus, click settings in the boot time scan area and make sure that the default action is move to chest(not ask). Then run the boot time scan again.
Title: Re: Possible false positive?
Post by: stitt on March 08, 2013, 05:26:56 PM
I really like latest version of Avast! It does seem to flag up some false positives though. Latest one for me is the new version of Furmark benchmarking tool.
everyone I have had has been found safe after a couple of updates, I turned the setting for reputation off if seems a little eager.
Title: Re: Possible false positive?
Post by: A. User on March 08, 2013, 05:42:12 PM
Report this to the Avast! virus lab.
Title: Re: Possible false positive?
Post by: spywar on March 08, 2013, 05:45:24 PM
I really like latest version of Avast! It does seem to flag up some false positives though. Latest one for me is the new version of Furmark benchmarking tool.
everyone I have had has been found safe after a couple of updates, I turned the setting for reputation off if seems a little eager.
You should not turn off Reputation service, it powers the autosandbox (mainly) !
Are you talking about FurMark 1.10.5 (http://www.softpedia.com/get/System/Benchmarks/FurMark.shtml) ?
I downloaded it, executed the setup and file got autosandboxed. It's a rare file in the community ...

spywar
Title: Re: Possible false positive?
Post by: stitt on March 08, 2013, 05:50:01 PM
I did report it to them, I alpha and beta test games so many programs I use have little or no reputation.
Title: Re: Possible false positive?
Post by: A. User on March 08, 2013, 06:59:56 PM
@twn321- if you create a topic in the viruses section attach this logs: http://forum.avast.com/index.php?topic=53253.0 (http://forum.avast.com/index.php?topic=53253.0)
Title: Re: Possible false positive?
Post by: twn321 on March 08, 2013, 08:36:16 PM
Well... Ran a boot time scan again today. And the system comes up clean this time around. Without the file ever having had anything done to it. Interesting...
Title: Re: Possible false positive?
Post by: A. User on March 09, 2013, 11:23:06 AM
Well... Ran a boot time scan again today. And the system comes up clean this time around. Without the file ever having had anything done to it. Interesting...
Maybe it's a false positive. Do you find the file? Are you sure that the file was not deleted when avast! find it? If you find the file upload it to the avast! virus lab!. How to upload files to the lab ->-> http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=1406#idt_07 (http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=1406#idt_07).
Title: Re: Possible false positive?
Post by: A. User on March 10, 2013, 07:26:16 AM
Win32:Malware-gen is a detection from the proactive part of avast!(heuristic engine, autosandbox, behaviour shield etc.). If you scanned the "infected" directory again with avast! and malwarebytes, and they can't find anything, it is likely to be a false positive. You can scan with Hitman pro to be sure: http://www.surfright.nl/en/hitmanpro/ (http://www.surfright.nl/en/hitmanpro/). Hitman pro is a cloud antimalware. It runs a behavioural scan and uploads the suspicious files to the hitman pro servers.
Title: Re: Possible false positive?
Post by: spywar on March 10, 2013, 09:54:11 AM
Quote from:  link=topic=117221.msg909590#msg909590 date=1362896776
Win32:Malware-gen is a detection from the proactive part of avast!(heuristic engine, autosandbox, behaviour shield etc.). If you scanned the "infected" directory again with avast! and malwarebytes, and they can't find anything, it is very likely to be a false positive. You can scan with Hitman pro to be sure: http://www.surfright.nl/en/hitmanpro/ (http://www.surfright.nl/en/hitmanpro/). Hitman pro is a cloud antimalware. It runs a behavioural scan and uploads the suspicious files to the hitman pro servers.
How do you know that any source ? Win32:Malware-gen is a signature generated by automated analysis systems, ATM behavior shield is mostly passive as it reports to virus lab all the suspicious binaries (CommunityIQ).
Title: Re: Possible false positive?
Post by: A. User on March 10, 2013, 11:10:01 AM
Take a look here: http://www.im-infected.com/trojan/win32malware-gen.html (http://www.im-infected.com/trojan/win32malware-gen.html)
 :)
Title: Re: Possible false positive?
Post by: spywar on March 10, 2013, 11:16:07 AM
Quote from:  link=topic=117221.msg909645#msg909645 date=1362910201
Take a look here: http://www.im-infected.com/trojan/win32malware-gen.html (http://www.im-infected.com/trojan/win32malware-gen.html)
 :)
This is not from Avast ...  ::)
It's mostly a signature generated by automated analysis system (like Win32:Rootkit-Gen or Win32:Dropper-Gen or Win32:Trojan-Gen) they are added very quickly, I can submit an undetected sample from program and 2 hours later it gets detected with one of these signatures.
Title: Re: Possible false positive?
Post by: A. User on March 10, 2013, 11:33:15 AM
Ok, then we need to help twn321 to get rid of this. He said that he can't find it in the "stdole" directory and in the virus chest. Do you think that avast! has deleted the threat or he is still infected ?
Title: Re: Possible false positive?
Post by: spywar on March 10, 2013, 11:36:47 AM
Quote from:  link=topic=117221.msg909663#msg909663 date=1362911595
Ok, then we need to help twn321 to get rid of this. He said that he can't find it in the "stdole" directory and in the virus chest. Do you think that avast! has deleted the threat or he is still infected ?
Avast! never delete file unless the user chose "Delete" instead of "Move to Chest" or he has deleted it from the virus Chest ...
Title: Re: Possible false positive?
Post by: Undead-Divine-Assassin on March 11, 2013, 04:26:40 AM
So has this Win32: Malware-gen thing been confirmed as a real threat or a false positive?

I'm still suspicious of it but I've had three different files being reported as Win32: Malware-gen by Avast and only using boot time high snesitivity scans. I used Avast's delete option to get rid of the first reported problem which was a file in my Restore Points folder. A new boot time scan afterwards was clean.

That was last weekend. This weekend I did another boot time scan and very quickly up came another case, this time in my Docs & Settings > All Users > Application Data folder. This time I sent it to the virus chest. Later that day I did another boot time scan and there was another reported Win32: Malware-gen this time again in the Restore Points folder but a different file from the previous deleted case.

As I knew where it was I found the folder and used both Spybot and then Malwarebytes to scan the folder. They reported nothing. I then tried a Quick Avast scan and that, which like the Full System scan I'd also done and had shown up nothing previously with this this or the earlier 'infections', was now also reporting the file as a virus.

Again I put it in the virus chest, repeated a boot time scan (clean), Quick scan (clean) and a full system Malwarebytes scan (clean). This morning I did a boot time scan at Normal sensitivity and that came out clean too.

That's where I am at but now no longer sure what to trust and not looking foward to doing a boot time scan at highest sensitivity in case it throws up another Win32: Malware-gen report somewhere else.   

   

I thought I'd check 
Title: Re: Possible false positive?
Post by: A. User on March 11, 2013, 07:02:25 AM
Quote from:  link=topic=117221.msg909645#msg909645 date=1362910201
Take a look here: http://www.im-infected.com/trojan/win32malware-gen.html (http://www.im-infected.com/trojan/win32malware-gen.html)
 :)
This is not from Avast ...  ::)
It's mostly a signature generated by automated analysis system (like Win32:Rootkit-Gen or Win32:Dropper-Gen or Win32:Trojan-Gen) they are added very quickly, I can submit an undetected sample from program and 2 hours later it gets detected with one of these signatures.
If it is signature based then it looks like it's not a false positive. But there still is a minimum chance to be a false positive.
Title: Re: Possible false positive?
Post by: DavidR on March 11, 2013, 03:28:04 PM
The win32:Malware-gen or win32:Trojan-gen are generic signatures (the -gen at the end), which are designed to detect multiple variants of the same malware type, this is why you see them on different files and variants, so it isn't a single signature detecting a single piece/variant of malware..