It would help to know what you downloaded and from whom (provide a link).
There's this site:
Flashback Trojan - Detection, and how to remove - http://www.f-secure.com/v-descs/trojan-downloader_osx_flashback_k.shtml
which has a link to a tool that you have to run as an application.
There's Apple's site where you run an updater (wither independently or through Software Update) which is also supposed to handle things.
Apple's Flashback removal and Java update for Intel Macs OSX 10.6 and 10.7- http://support.apple.com/kb/HT5242 actual file at: Java for OS X Lion 2012-003 - http://support.apple.com/kb/DL1515