With the threat of the worm that is set to "explode" on the 3rd it is a good thing to have your antivirus updated. if you do not have an active antivirus there are free ones out there that is much better than nothing. here is a link to a good one. it is full function for 14 days. after the trial is over you can still update and scan. the only difference is there is no real time protection after that date. It is a good one to have. it is called
Ewido
another good one is Avast 4 Home Edition.
HERE This one is totally free and totally full function. checks for updates every time you turn on your puter.
You can also use both at the same time.