An update has been released which fixes an issue that allows malicious clients to cause game-servers to crash. If you don't want this to happen to your server, you should update it. All dedicated servers should be updated through either your Game Server Provider's control panel or SteamCMD. Edit: If it says 'content file is locked', contact Steam Support for help. http://support.steampowered.com/ Your free antivirus is most likely deleting the game or update files causing it all to die. Add Steam to your AV exclusions, restart Steam, and try updating again.