Just to add some further info: Windows Viruses do not affect Linux OS's.
The reason behind using an AV scanner in your Linux Distro is to stop the transmission of viruses to our friends who are running a Windows OS.
Therefore as Tech said:
Yes, the virus definitions are the same and the engine could detect Windows viruses.
Security compromise under Linux / Unix can be more a User fault rather than a Virus, in most cases.
