Today we detected a new variant of IM-Worm.Win32.Kelvir - we detect it as Kelvir.k. As always Kelvir is accompanied with an IRCBot, which we detect as Backdoor.Win32.Rbot.gen.
This new Kelvir variant uses a new social engineering tactic to spread. Instead of hyperlinking to, for instance, a .pif or .scr file, Kelvir.k links to a .php file. The thing about links to .php files is that you can append extra data (letters and numbers) to them. This additional data will be sent to the server when the link is clicked. And that's exactly what Kelvir.k does - it appends the IM user's MSN address to the link.
To make things a bit clearer, here's an example.
IM user #1 has the email address firstname.lastname@example.org
IM user #2 has the email address: email@example.com
User #1 gets a link which looks like this: hxxp://www.[edited].us/[edited]/firstname.lastname@example.org
User #2 gets a link which looks like this: hxxp://www.[edited].us/[edited]/email@example.com.
When the link is clicked, the user is presented with a prompt to execute or save an MS-DOS application. By now, users will hopefully be suspicious and not run the application.
But as soon as the user clicks the link, their email address is harvested. So even if the user doesn't run the MS-DOS application, the brains behind Kelvir get another address to spam.
So is this new tactic being used because of MSNM 7's new 'anti-malware' features? I don't think so. While I was writing this, we detected a repacked version of Kelvir.e. And Kelvir.e uses a hyperlink to a .scr file to spread, something which isn't filtered by MSNM 7.
The use of new social engineering tactics leads me to believe that IM-users have learned to be more careful - 'traditional' IM-Worms don't seem to be as effective as they used to be, and attackers are looking for new ways to install their malware on a large number of machines.
We have seen an increase in IM-Worms over the last couple of weeks.
Yesterday we saw two new Bropia variants.
We also saw a new version of IM-Worm.Win32.Kelvir.a, packed with a hacked version of UPX, which made it undetectable for most AVs.
And we just released an urgent update for IM-Worm.Win32.Sumom.a, which also included an update for IM-Worm.Win32.Kelvir.b.
The vast majority of IM-Worms currently make use of MSN and they normally 'arrive' as a (web)link to a picture, which of course isn't a picture but an executable.
Paris Hilton has the been subject for these IM-Worms quite a lot of times, along with other topics.
Attackers are using social engineering techniques once again.
Most IM-Worms have got a .pif extension and what I'm hearing a lot is that people are mistaking the .pif for a .gif or .tiff format, which are pictures.
Note that almost all current IM-Worms also install a Backdoor on the system which gives the master control over the infected systems.
We have seen cases where IM-Worms were used to install AdWare onto the infected system.
The bottom line? Next time someone sends you a link or file via IM, check it closely. A .pif file will certainly mean trouble.
Also ask the person if he is aware of sending that link or file. This will give you more insight into if the file is possibly malware, and in the case of a worm, will also alert the sender that he's infected.