Java Agent infections

My sister’s computer is a Windows 7 machine with Avast antivirus. We always keep it updated also. Anyway earlier Avast did a boot up scan and found all sorts of Java: agent- related infections. I told Avast to move all the infected files into quarantine but I’m wondering how did this occur and did the Avast scan grab everything? I’m getting a little tired spending an entire day (or more) reformatting/restoring machines when they get corrupted so if there’s another way to clean the system someone please tell me. I’ll be glad to provide any log files needed.

I'm getting a little tired spending an entire day (or more) reformatting/restoring machines when they get corrupted so if there's another way to clean the system someone please tell me.
you already did when moving it to avast chest.......why reformat ::) guessing these where classified as exploits.....and found in java cache ? is latest java installed?

you can empty java cache with a little program like CCleaner…it will also clear lots of other crap files