How to remove Java.Trojan.Downloader.Toniper.A from my iMac?

My iMac was running a bit slow and acting weird (launchpad went crazy etc.). I ran a virus scan with BitDefender and found this trojan (Java.Trojan.Downloader.Toniper.A) from my computer. I did some research and found out that it's a severe trojan for Microsoft that downloads other viruses and also tries to get my passwords etc. I really want it to be removed from my Mac but I have no idea how.. I didn't find any discussions about this trojan on OS X.

Any advice for me ? I already got mailed that someone has tried to log in to my Google-account.... Please, help!! 😢

The computer is iMac 21,5'' mid 2011 and Mac OS X Lion 10.7.5