Graps worm was discovered in the beginning of July 2003. This worm spreads in local networks. It scans a network for vulnerable computers and tries to get access the IPC$ and ADMIN$ shares by performing a dictionary attack (using a set of pre-defined weak passwords to get access). If the worm succeeds, it copies itself to remote computer, activates its file and deletes IPC$ and ADMIN$ shares.
To disinfect a system it's enough to delete mwd.exe file and 3 above mentioned batch files from a hard disk.
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The worm is a 53kb Windows PE executable file written in Visual Basic and compressed with UPX file compressor. The worm spreads itself with the help of the following files:
psexec.exe - a utility that allows to run processes on remote computers mswinsck.ocx - standard WinSock library for VB applications wds.bat \ wds2.bat - batch files that spread the worm to remote computers (dropped by the worm) wds3.bat / mwd.exe - the worm's executable file
The batch scripts that the worm drop are used to get access to IPC$ and ADMIN$ share protected by a weak password or no password at all. When such a share is discovered, the scripts copy the worm's main file mwd.exe and also psexec.exe and mswinsck.ocx files to \ADMIN$\System32\ folder (which is a Windows System folder on a remote computer) and start the worm's file remotely with psexec.exe utility. As a result a remote computer becomes infected with the worm. After spreading the worm tries to delete IPC$ and ADMIN$ shares.
On an infected computer the worm creates a startup key for its file in System Registry:
[HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run] "Windows Management Instumentation" = "%winsysdir%\mwd.exe"
The worm has a few additional features. It listens to the specific port and can allow remote hackers to log into it and perform the following actions:
- perform DoS (Denial of Service) attack - get system information - search for specified files on a hard disk - redirect traffic (works as a proxy) - scan for open ports