There is a particularly malicious set of malware that is targeted at Macs.
It’s got several derivative names of MacDefender or MacGuard. It disguises itself as an Anti-virus program that has found a virus on the computer. It urges the user to buy a product to have virus removed.
The current method to avoid the virus is to disable “Open Safe Files After Downloading” in Safari or your current browser. At the moment, the virus still has to be installed by the user so don’t automatically install anything that you are not specifically trying to install. The current variant no longer requires a password.
If you’re already infected, here’s a link to Apple’s support page for this issue.
Of course forums are where the real treasure is. For more help try here: