The only way to be sure nasties are gone is to reformat your system and reinstall the operating system, then restore files from the backups you're diligently doing as you should.
Anything else and you're basically just burying your head in the sand and hoping you've found everything.
There's no way I'd do my online banking on a previously infected computer unless it had been wiped and reformatted.
Prevention is the best cure when it comes to computer viruses, its not exactly difficult to avoid infection .... unfortunately most users are lazy and click on stuff etc. without considering the repercussions.