Comment Sniff for suspicious traffic on a regular basis (Score 1) 295
Critics about why this got posted aside, I use NetworkLog (formerly IPTablesLog) to check what's the traffic generated by my installed applications from time to time (and send the one I don't trust to 127.0.0.1 in the /etc/hosts or block it via a firewall). There's also another application for network troubleshooting on SourceForge, but I haven't tested it.