Android Man eluded in his playlist post in Announcements section about going to playlist sites and getting viruses and adware. If you have a Mac you want to get ClamXa/v for the few viruses around, never found a Mac virus yet, and AdwareMedic.
Just like PCs, Macs are subject to adware. One thing to avoid with Mac is MacKeeper. Never, NEVER download that program. It's the worst.