Quote:
This is a Windows 95/98 and NT virus that infects PE EXE files. It is a polymorphic, per-process resident and direct-action infector. The virus is encrypted in the host file and will be decrypted by a small decryptor consisting of random opcodes. The direct-action infection is fast: when an infected file is run, the virus goes through all the PE files in the various directories for infecting them.
The decrypted virus body contains strings of Windows API functions and directories used by the virus:
CreateFileMappingA, CreateThread, DeleteFileA, DosDateTimeToFileTime, FindClose, FindFirstFileA, FindNextFileA, GetCurrentDirectoryA, GetDriveTypeA, GetFileSize, GetLocalTime, GetTickCount, FileTimeToDosDateTime, MapViewOfFile, SetFileAttributesA, SetFileTime, UnmapViewOfFile, _llseek, _lopen, _lread, _lclose, _lwrite
C:\NTLDR
C:\WINNT\system32\ntoskrnl.exe
C:\WINNT\system32\MSV1_0.dll
\WINDOWS\Cookies\*.*
\WINNT\Cookies\*.*
If the administrative privileges are present, W32/Bolzano.l modifies NTOSKRNL.EXE and NTLDR.EXE in order to preserve these rights in some future sessions. With this trick it would be then possible for the virus to infect any file on an NTFS volume even only with Guest rights. The AVERT however did not try to produce this behaviour.
W32/Bolzano.l deletes the files in the Cookies sub-directory.
The a, b, c, h and i variants of this virus are simple PE appending virus and are not crypted.
The d variant does not replicate well and is nearly intended.
W32/Bolzano.e, f, g and l patch multiple CALL's in the host's code to point at the virus body instead of modifying the PE executeable's entry point.
The variants e, f, g and l are polymorphic viruses.