You, are your own BEST firewall and antivirus for your
PC/laptop.
If you can't get by without using any of those music file sharing
programs, you can use Commercial Standard hardware firewalls and
you'd still corrupt your system.
By Home User standards, Norton Internet Security 2005 (Spyware
Edition) will suffice.
Adware Removers and whatever that is FREE downloads from the
internet, are all spyware and adware also. REMEMBER: nothing good
is FREE, while the good stuff are NOT free.
Then again, if continue to download and share MP3 files, don't
waste money buy NIS2005. You'd still get infected.