virus or scam

Definitely a scam. The "Your system in infected with 3 viruses!" message is a common one that is been going around for at least a year now. Funny how it's always just 3 viruses. Don't be fooled, and definitely do not click on the "Scan Now" link.

I saw one that said the OP's Mac was infected with over 200 viruses, lol!

No one can know what's on your Mac, not even Apple.

Scam.