Just to clarify, there are three different updates, each for a different subset of users. The update mcbuffy mentioned is only applicable to users of Lion who do not have Java installed. Rather than try to figure out which one is right for you, just run Software Update and install whatever Java- or Flashback-related update is available. If, after running it, you are told that you had Flashback, then you were infected and it has been removed. If not, you were not infected. Either way, you will be safe in the future from any other malware trying to use the same Java vulnerabilities.