EC0-350 Question #26: Real Exam Question with Answer & Explanation

You receive an e-mail with the following text message. "Microsoft and HP today warned all customers that a new, highly dangerous virus has been discovered which will erase all your files at midnight. If there's a file called hidserv.exe on your computer, you have been infected and your computer is now running a hidden server that allows hackers to access your computer. Delete the file immediately. Please also pass this message to all your friends and colleagues as soon as possible." You launch your antivirus software and scan the suspicious looking file hidserv.exe located in c:\windows directory and the AV comes out clean meaning the file is not infected. You view the file signature and confirm that it is a legitimate Windows system file "Human Interface Device Service". What category of virus is this?