RingZero is a trojan. It can arrive as an executable e-mail attachment. This trojan first arrived attached to a Winsock Version Checker program. The pure trojan has 2 parts - an executable part (an EXE file packed with Petite file compressor) and a small VXD part attached to executable. The trojan can be also attached to any Windows executable.
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When the trojan is run it first installs itself to system. It detaches itself from a file it came with and writes 2 files to \Windows\System\ directory. One file is always RING0.VXD and the other can have different names:
TELNET23.EXE EXPLUPD.EXE PCT.EXE ITS.EXE
Also the third file called A.EXE could be created. Then the trojan makes necessary modifications so it could be always run with Windows. Being active the trojan scans Internet for proxy servers and if such server is found the the trojan writes its address to ITS.DAT (or to differently named DAT file) and sends this file to a website with the following address: www.rusftpsearch.net (now it is removed for security reasons).
It seems that the trojan was purposely created to send data to that server. The idea was most likely to collect information about all proxy servers on Internet and compile it into a database.
The trojan doesn't have any other payload and it doesn't work on Windows NT.
Description Created: Mikko Hypponen, F-Secure
Technical Details: Alexey Podrezov, F-Secure