Do you hate the MPAA / RIAA and other company’s that spy on your download behavior? Are you tired downloading fake chunks of a file? Then it’s probably wise to cover your arse by installing peerguardian or protowall. This will keep (most of the) the bad guys out.
Peerguardian and Protowall serve as “mini” firewalls and block ip’s of potential intruders. The so called blocklists are updated daily and can be edited to your needs.
Both applications seem to do the job. However installing Protowall is a bit more complex for most people. If you’re still on a 486 with 32mb ram Peerguardian “Lite” is probably the best option.
note: Most BitTorrent clients can handle blocklists without using Peerguardian or Protowall. But make sure these lists are up-to-date then