This assumes that your clients are not accessing through a proxy. A proxy could introduce one of two "problems" to this...

• Multiple clients come through the same proxy
• One client can come through multiple proxies

Situation 1 could happen with a large provider (AOL, for example). Situation 2 could happen with a farm of load balanced proxies / NAT / firewalls.

Point being that this could generate some false positives (from a hack detection view), but if you can live with that, then yes, jsegal's suggestion does have merit :)

--MidLifeXis