This article is pretty self-explanatory:
Mac: Your System Is Infected With (3) Viruses, Fix
I want to add this:
The BEST protection that you can provide to your Mac is NOT adding antivirus programs, or paying for scamware like MacKeeper.
Just keep updating the operating system.
Every Apple device has an invisible program running called Gatekeeper. It checks in with Apple twelve times away, to make sure that you are being protected on a very deep level. That part is automatic. However, in order for your safety, privacy and peace of mind, Apple also updates a lot of other components as time goes by.
For instance, I always talk folks out of using Chrome or Firefox web browsers, because Safari is the best (at the moment) at circumventing cookies and malicious tracking of your every move online. Also, if everything is set up right, if Safari saves your passwords at every opportunity (I recommend it), then the same password is now available on your iPhone and iPad in about fifteen seconds.
I’ve written about this next security topic before, but it bears repeating:
Do NOT believe the tricksters who will lie to you, saying “Your Flash Player needs updating – Click HERE!” I just helped a client yesterday who had SEVENTY THREE copies of the Flash installer on her computer. Many of them are pre-loaded with adware, scamware and crapware.
She called me begging for help in getting rid of whatever was making her web-pages go crazy with unwanted ads. While doing so, I told her this:
Here is the ONLY safe way to make sure that your Flash player is updated safely, in my opinion:
– Pull down the Apple menu, and choose System preferences.
– Go to Flash Player on the bottom row.
– Click on Updates at the top.
Form there, it’s pretty self-explanatory.