If you have a Mac computer, you may have heard about the Mac Flashback malware that’s affected some 600,000 machines.

So what is it, how can you tell if you have it, and — most importantly — how can you get rid of it?

First, it’s important to note it isn’t a virus in that it can’t infect other computers. It’s a Trojan horse, meaning you have to install something to activate it — in this case, most experts think the Flashback malware first appeared in September of last year, masquerading as an innocent Adobe Flash Player plug-in.

Once a Trojan horse is installed, it then goes about its dirty work of stealing data (like your website passwords), and you may never know a thing.

To see if your machine has the Flashback malware, CNET and other sites recommend using Dr. Web’s online utility. If you have the trojan, CNET has also posted a step-by-step removal guide.

After you’ve cleared it off your computer, it’s a good idea to change your website passwords for financial institutions and other secure services that you may have used while your machine was compromised. And in the future, only download add-ons and plug-ins from trusted sources.