mssys.exe definition, relationships, removal:

mssys.exe is an executable file that starts a malicious process, launches certain parasite components or runs a destructive payload. Even if the mssys.exe file does nothing suspicious, its presence indicates that your computer is infected with a particular threat.
The mssys.exe file is installed and used by trojan Trojan.Myss.B.
Sometimes a presence of mssys.exe 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 mssys.exe before completely deleting or leaving it in the system.