You just set up a security system in your network.

Snort is an open source network intrusion detection system (NIDS) for networks .

Snort rule example:

This example is a rule with a generator id of 1000001.

alert tcp any any -> any 80 (content:"BOB"; gid:1000001; sid:1; rev:1;)

References: http://manual-snort-org.s3-website-us-east-1.amazonaws.com/node31.html