Apple advise that virus protection should not be required if you keep your Mac OS up to date. In fact many supposed protection software grab lots of processor & RAM slowing Macs down by interrupting OS X system calls. If you are still worried go App Store and download free ClamXav and run once a month or if you are worried.
iMac 20” upgraded to Mavericks & running like a dog, even after RAM upgrade to 6GB. No faults HD or software updates. Checked logs and Kaspersky is creating excessive activity. Get rid of it. BUT deleting the app leaves residue & still a problem. Download Kaspersky uninstaller.