Tuesday, February 17, 2009

Virut and other File infectors - Throwing in the Towel?

I actually wanted to blog about this last week, but didn't find the time yet...
In the last couple of weeks, I noticed a HUGE increase of Virut present on computers. As a matter of fact, 30% of the infected computers I analyzed were infected with Virut. This is bad, really bad... :-(

Virut is a Polymorphic File Infector that infects .EXE and .SCR files. It opens a Backdoor by connecting to a predefined IRC Server and waits for commands from the remote attacker - for example to download/run more malware on the compromised computer. Emails may be harvested as well.
This latest variant may also search for htm, html, asp and php files on the drives and modifies them by inserting an iframe that points to a malicious website. So you can already imagine what may happen if the owner is a webdesigner and uploads the infected webpages.
An excellent write up on this latest variant (and previous one) can also be found here (by Nicolas Brulez): http://securitylabs.websense.com/content/Blogs/3300.aspx

Disinfection of the infected webpages should be easy - it's just a matter of deleting the iframe script in it.
The disinfection of the infected exe and scr files is something else...
Since Virut infects legitimate files, the files may not be deleted, but disinfected instead. And that's where the problems start...
Virut was known to be a buggy Virus in the past and it appears that this hasn't changed yet. We've seen this with other File infectors as well: To Junk Or Not To Junk.

And because of that, Virut may misinfect a proportion of executable files > result > corrupted file.
The same applies for other File infectors such as Sality.

If I guide someone with Virut (or any other File Infector) present and their Antivirus cannot properly disinfect it, then I recommend a format and reinstall.
And even though an Antivirus is able to disinfect the files, in a lot of cases, many files will be corrupted anyway > result > many programs won't work > loads of errors > corrupted Windows + there's still no guarantee that the Virus is really gone.
So why bother to clean this if a format and reinstall is the fastest and especially the safest solution?

And that's why I am blogging about this in the first place, especially since Virut is a very common infection nowadays. It's a pity to see that so many people are struggling with it and whatever they try, nothing helps. Then they ask for support via the forums and in a lot of cases, the one who is helping/guiding won't give up either and posts a new set of instructions to deal with this one.
Unfortunately another failure as result, so again, new instructions are posted... and this may go on and on...sometimes for weeks....
Is this responsible?
I'm not saying it fails everytime, but from what I have seen so far and especially if you're helping someone else with this infection... don't guarantee them a "clean" and errorfree computer afterwards .

In anyway, that's how I see it. Imho, dealing with such infections is a waste of time and that's why I prefer the fastest and safest solution - which is a format and reinstall.
Many people may see this as "giving up", but I see this different.
After all, I think it would be irresponsible to let the malware "stew" (download/spread/run more malware) for another couple of days/weeks if you already know it's a lost case.

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