St. Louis (KSDK) - If you're a Mac user, you probably think your computer is safe from computer viruses.
But there'slots of talk on social media about the Flashback Trojan.
It's malware that's infected about 600,000 Macs.
The news is coming as a shock to many Mac users who thought their computer was safe.
We talked with a concerned Mac user and a Mac expert on First @ 4.
Click on the video player above to watch.