Java is not installed by default on OS X v.10.7. If you didn't install it you don't have to worry.
If you don't know, you can still use the Flashback malware removal tool released by Apple :
For more info about that malware you can read this page :
Hope this will help.
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.
This morning while getting mail I had the Little Snitch monitor window open and noticed something called cloudfront.net downloading. I've read that there is malware by this name and that it is also something that Amazon does. Should I be worried?
I'm on OS X Mountain Lion 10.8.4, intel 24" iMac 2009