Downloader Infection

I ran Norton Antivirus on Thursday and all it found was 1 cookie. I ran it again yesterday (both out of my normal scheduled scan) and it found that Downloader had infected 2 files in Java. Does this mean that Downloader got onto my computer between the scans, or did the virus definitions update on Friday allow the antivirus to find something it couldn't find on Thursday? The virus listing seems to suggest that all versions of Downloader were known about some years ago - or did I get a new version?

 

Best wishes,

 

Bill