Ubuntu Security :: 11.04 - Automated Email With Unclickable Link

I'm fully aware that Linux, and Mac OS X are a far reach from Windows when it comes to viruses. I run Xubuntu 11.04 on the netbook, and Mac OS X 10.4 on a Mac Mini. But, and I now wish I kept the email and didn't delete the account, but the following happened recently: I received an email, from myself (I was on my own contacts list) that was sent to a few others on my contacts list - an email I did not send out. There was no subject, and an unclickable link that - once copy/pasted and gone to, was "Forbidden," even when you took the /s away and went to the main site, it was "Forbidden." It was a .be website (Belgium). Being that one of the recipients was "noreply@craigslist.com" I can only assume that this email was automated.

It was only sent to a few addresses, all of which were tied to my account. I changed the password, deleted my contacts, and deleted the address (and have a new one elsewhere). I ran ClamAV on here, an antivirus on my Mac Mini (and I'm running a different one now), and thus far, absolutely nothing. So my question is - Is it, then, even reasonably possible that either of my computers are infected, and if not, how did this occur? I'm just taken aback a little, considering I don't use or have Windows on any machine that I own, and extremely rarely use Windows when elsewhere (and not at all recently).