I use AOL for my email. AOL froze my email acct because they said it sent out multiple emails that were not normal activity on my acct. They said I probably opened an email that triggered this activity and I should check my computer for viruses and malware.
While there are a few types of malware which can affect a Mac (a few Trojans, one worm, and a few Java exploits), there is not, nor has there ever been a virus that works in OS X.
Far, FAR more likely is someone hacked into your AOL account and is using your email to send out spam. Go into your account and immediately change your login and email passwords.