Having a virus in a laptop such as a mac is usually rare. But in these days of downloading, file sharing, people download things from all over the internet with no place to check wether it is safe or not. This can lead to virus' getting in our laptops because we could be expecting an app o be downloading whereas actually, if the download is a .ZIP or .DMG file then as soon as they are opened, the virus would go into the hard rive and basically take over it.
Sometimes it takes time for a virus to take over your laptop or maybe instead of going to take over data, It wants to do something else. This would make your mac slow down a lot and could be a sign of a virus.
So My mac started to get very slow and I just thought of doing a virus scan. It was scanning my whole laptop and so I left it to run overnight. When I checked later on, It showed that I had three files that had a risk of being a virus! This app was very good though and "Quarantined" the files by moving them to a certain location like the desktop. From there I managed to see what the virus' was and if I could, then delete it. I managed to delete the virus and my laptop actually started to run faster.
I ran the virus scan overnight on four virus scanning apps all free from the app store:
Only ClamXav and Virus Barrier express found virus'. If you only want one virus scanning app then I would recommend Virus barrier express since it shows what file was the virus and put's it straight into the trash.