winlog.dat definition, relationships, removal:

This is a part of a malicious parasite that violates user privacy and damages the compromised system. The winlog.dat file can be used for different purposes depending on the related parasite's type, functionality and carried payload. Although winlog.dat may not take any malicious actions by itself, it ensures that a parasite is working properly and therefore needs to be removed. DO NOT open, execute or edit winlog.dat!
The winlog.dat file is installed and used by keylogger JanNet.
Sometimes a presence of winlog.dat does not indicate that your computer is infected. It can be an essential system file or a file installed by harmless legitimate software and therefore may not pose any threat to your privacy and the system. Although such cases are quite rare, you should thoroughly examine winlog.dat before completely deleting or leaving it in the system.