manual method:
http://arstechnica.com/apple/news/2012/04/how-to-check-forand-get-rid-ofa-mac-flashback-infection.ars
software method:
http://osxdaily.com/2012/04/09/detect-flashback-malware-easy-mac-os-x/
apple released an update you should install:
http://support.apple.com/kb/HT5244
http://arstechnica.com/apple/news/2012/04/how-to-check-forand-get-rid-ofa-mac-flashback-infection.ars
software method:
http://osxdaily.com/2012/04/09/detect-flashback-malware-easy-mac-os-x/
apple released an update you should install:
http://support.apple.com/kb/HT5244