Variants in the IM-Worm:W32/Sohanad family are worms that spread via instant messaging software, primarily Yahoo Messenger.
Sohanad variants were first encountered in late 2006 targeting Vietnamese users of Yahoo Messenger. Not all later variants have their roots in Vietnam, but Sohanad variants are still largely written by and target Vietnamese Internet users.
Sohanad variants are written with AutoIt scripting language.
Sohanad worms use Instant Messenger programs such as Yahoo! Messenger to propagate. When a Sohanad worm on an infected computer detects that Yahoo Messenger is running, it sends a message to the people on the victim's contacts list.
The message includes a URL that direct to a location containing a copy of the worm. Once the recipient of the message clicks on the link, he ends up downloading the worm.
The messages themselves use varying types and levels of social engineering to appear interesting to potential victims. The following are some of the English messages used by Sohanad variants:
- oh my god , i've won a 20000 usd lottery :O http://lottery-news.info/?id=winning_list . Come to my house tonight for a party !! >:D<
- Images shot in Iraq _ The war will never end http://thecoolpics.com/Iraqwar.jpg << :(
- :D who is beside you in this pic http://thecoolpics.com/friendpic1.jpg so good-looking
- Screenshot of new windows version _ Windows Vista http://thecoolpics.com/vista.jpg so cool :D
The file names are not actually part of the URL, but are just included in the messages to make them appear more legitimate.
Some variants also use other Instant Messengers to spread themselves such as AIM, Windows Live Messenger, or Windows Messenger.
Once downloaded onto the computer, the worm copies itself somewhere on the system under a name that is meant to be inconspicuous. Examples:
Note: %windir% represents the system's Windows folder.
Sohanad variants also create a registry entry that executes the worm at startup. Typically Sohanads also modify the registry to disable task manager and registry tools. Examples:
- # HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\system DisableTaskMgr = 00000001
- # HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\system DisableRegistryTools = 00000001
Members of the Sohanad family often try to end other processes, usually antivirus or other security software.
Other possible targets include Windows Task Manager and Registry Editor.
Some Sohanad worms are also able to change the Internet Explorer home page, download other malware, or spread as an AutoRun worm.