Over 600,000 Macs are infected with the FlashBack Trojan. Is yours one of those? Let’s find out.

Open the Terminal (c’mon, be a hacker, not a slacker) and type:

defaults read /Applications/Safari.app/Contents/Info LSEnvironment

if it says:

The domain/default pair of (/Applications/Safari.app/Contents/Info, LSEnvironment) does not exist

that means your Mac is ok so far (otherwise, go here). 

Then type:

defaults read ~/.MacOSX/environment DYLD_INSERT_LIBRARIES

if it says:

The domain/default pair of (/Users/[your user name here]/.MacOSX/environment, DYLD_INSERT_LIBRARIES) does not exist

that means your Mac is not infected (otherwise, go here). 

Source FSecure via Ars Technica.