It should be expected that all p2p users have protection software on their computers.
Recommended are:

1. A reasonable anti-virus softw. with updated virus definitions.

2. ad-ware http://www.lavasoftusa.com/software/adaware/

3. Spybot - Search & Destroy http://www.safer-networking.org/en/mirrors/index.html

4. Peerguardian: http://peerguardian.methlabs.org/pg2.html

* Try to avoid downlding .exe files thru p2p. Instead find zipped files. Scan them before use.