With a percentage of 8.15, the second e-threat on December’s Top Ten is Trojan.AutorunInf.Gen, a generic mechanism to spread malware using removable devices such as flash drives, memory cards or external hard-disk drives. Win32.Worm.Downadup and Win32.TDSS are two of the most famous families of malware to use this approach to trigger newer infections.
Trojan.Clicker.CM is in this month’s number three position with 7.90 percent of the total amount of infected computers and is mostly found on websites hosting illegal applications such as cracks, keygens and serial numbers for popular commercial software applications. The Trojan is mostly used to force advertisements inside the users’ browser in order to boost their advertisement revenue.
Ranking fourth in this month’s e-threat report, Win32.Worm.Downadup.Gen is responsible for 5.85 percent of the global infections. Relying on the Microsoft Windows Server Service RPC Handling Remote Code Execution Vulnerability (MS08-67), this worm spreads on other computers in the local network and restricts users’ access to Windows Update and security vendors’ web pages. Newer variants of the worm also install rogue antivirus applications, among others.
Trojan.Wimad.Gen.1, ranking fifth with 4.57 percent of the global infections, mostly exploits the capability of ASF files to automatically download the appropriate codec from a remote location in order to deploy infected binary files on the host system. The ASF format will store data in either WMA (Windows Media Audio) or WMV (Windows Media Video) formats, which are mostly to be found on Torrent websites. When played locally, the specially-crafted WMV file would allegedly attempt to download a “special codec,” which is in fact a malicious binary hosted on a third-party website.
The sixth place with 2.65 percent of the infections triggered globally is taken by Win32.Sality.OG. This malicious e-threat is a polymorphic file infector that appends its encrypted code to executable files (.exe and .scr binaries). It deploys a rootkit and kills antivirus applications running on the computer so as to hide its presence on the infected machine.
Trojan.Autorun.AET, a malicious code spreading via the Windows shared folders, as well as through removable storage devices, ranks seventh with 1.97 percent of the worldwide infections. The Trojan exploits the Autorun feature implemented in Windows for automatically launching applications when an infected storage device is plugged in.
Worm.Autorun.VHG is an Internet /network worm that exploits the Windows MS08-067 vulnerability in order to execute itself remotely using a specially crafted RPC (remote procedure call) package (an approach also used by Win32.Worm.Downadup). The worm ranks eighth with 1.65 percent of the global infections.
Win32.Worm.Downadup.B ranks ninth with 1.08 percent. It is a variant of Win32.Worm.Downadup with slightly the same functionality, except for the fact that the number of the blocked AV URLs is lower. Also, this is one of the least dangerous variants, as it comes with no malicious payload.
BitDefender’s December 2009 Top 10 E-Threat list includes:
1 Exploit.PDF-JS.Gen 12.04
2 Trojan.AutorunINF.Gen 8.15
3 Trojan.Clicker.CM 7.90
4 Win32.Worm.Downadup.Gen 5.85
5 Trojan.Wimad.Gen.1 4.57
6 Win32.Sality.OG 2.65
7 Trojan.Autorun.AET 1.97
8 Worm.Autorun.VHG 1.65
9 Win32.Worm.Downadup.B 1.25
10 Trojan.Script.236197 1.08