There are many forms of ‘Malware’ that can affect a computer system, of which ‘a virus’ is but one type, ‘trojans’ another. Using the strict definition of a computer virus, no viruses that can attack OS X have so far been detected 'in the wild', i.e. in anything other than laboratory conditions. The same is not true of other forms of malware, such as Trojans. Whilst it is a fairly safe bet that your Mac has NOT been infected by a virus, it may have another security-related problem, but more likely a technical problem unrelated to any malware threat.
You may find this User Tip on Viruses, Trojan Detection and Removal, as well as general Internet Security and Privacy, useful:
The User Tip (which you are welcome to print out and retain for future reference) seeks to offer guidance on the main security threats and how to avoid them.
More useful information can also be found here:
The Helpful Hound wrote:
What is the best or most compatible security software for iMac?
ClamXav as it gets updated often and doesn't install itself, it's a run as you need it to clean the Windows malware off.
Mac malware is rare and none of the commercial products have caught the few ones we do get.
For 10.8 your going to have to first head to System Preferences > Security and Gatekeeper to "Anywhere" to download software from the Internet.
If you mean security in the sense of personal privacy?, forget it.
The Mac is a snitching rat machine as well as everything online and nearly everything connected to it, especially your smartphone.
Read the Paranoid Section here, it will shock you