Safari running slow and unusual windows appearing. You may have malware installed called adware. Remove by downloading the free Adware Medic. It updates every time you use it & if it helps plea make a donation when you use it.
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.