Worm:Win32/Gaobot

When Win32/Gaobot.worm runs, it copies itself to either the Windows or System directories. In many cases, it adds a value to the registry keys:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

or
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices

This value causes the worm to start when Windows is started. Some variants may also add a Windows Service to attain similar results.

 

Win32/Gaobot.worm connects to a remote IRC server and joins a specific channel to receive commands. These commands can include actions such as scanning for unpatched machines on the network, downloading and executing remote files, adding and removing local users, retrieving the machine configuration, and updating the worm.

 

The worm spreads to remote machines by exploiting one or more of eight vulnerabilities. For example, the worm exploits the MS03-026 vulnerability to create a remote shell on the target machine. The worm uses the remote shell to copy and run the worm on a remote machine. The worm uses the eight different vulnerabilities in different ways, but the goal of the worm is consistent: it always attempts to copy and run on the remote machine.

 

Win32/Gaobot.worm may also spread to machines with weak passwords by using a list of specific passwords until it gains access. The worm then copies itself and creates a task on the target machine to run the copy.

 

Some variants of the worm terminate security products, based on a list of process names.

 

Later variants of the worm include user-mode stealth, which hides the worm process and file from Task Manager and Windows Explorer.

 

Later variants of the worm overwrite the Windows host file to block access to different security Web sites.