W32/Virut.h is a polymorphic, entry point obscuring (EPO) file infector with IRC bot functionality. It can accept commands to download other malware on the compromised machine.
It appends to the end of the last section of executable (PE) files an encrypted copy of its code. The decryptor is polymorphic and can be located either:
- Immediately before the encrypted code at the end of the last section
- At the end of the code section of the infected host in 'slack-space' (assuming there is any)
- At the original entry point of the host (overwriting the original host code)
The decryptor will either receive control directly or an API call within the host code body will be overwritten to point to it (EPO technique). In all cases where host code is overwritten by the virus the original bytes are stored within the encrypted virus body, and are restored before transfering control back to the host. This virus may also infect the files multiple times.
Indication of Infection
- Modified executable files (increase in the size of exe files)
- DNS queries to eircd.zief.pl and IRC related network traffic
Methods of Infection
W32/Virut.h is a file infecting virus. Infection starts with manual execution of the binary. Executables in network shares may also get infected if accessed by the compromised machine.
The virus has a number of bugs in its code, and as a result it may misinfect a proportion of executable files. In those cases of misinfection in which repair data is present within the virus body, and has not been miscalculated by it, the current DAT set will repair the virus as per the non-corrupted case. However, unfortunately, some W32/Virut.h infections are corrupted beyond repair.