You can check if your Mac is infected with Flashback Trojan or not with the following Terminal commands.
Launch Terminal (/Applications/Utilities/) and enter the following commands:
defaults read /Applications/Safari.app/Contents/Info LSEnvironment
defaults read ~/.MacOSX/environment DYLD_INSERT_LIBRARIES
If your machine answer is:
“The domain/default pair of (/Applications/Safari.app/Contents/Info, LSEnvironment) does not exist”
“The domain/default pair of (/Users/joe/.MacOSX/environment, DYLD_INSERT_LIBRARIES) does not exist”
then your Mac is clear.
See more detail on osxdaily.com
If you don’t like Terminal commands and you prefer to use an app instead then read the following article and download Download FlashbackChekcer.