Todays network outage was caused by a denial of service attack known as a "smurf" attack. In this type of attack, the attacker finds a network with high bandwidth, a lot of hosts, and open network broadcast addresses (all sites SHOULD have ICMP blocked to their broadcast addresses). They then fire off rapid ICMP echo request packets (essentially a ping) with the source address forged to be the address of the target machine. This causes EVERY machine on the intermediate network to send an ICMP echo request to the forged source address, which in this case was one of our machines (chat). In this particular case the volume was so heavy that it totally saturated both T1's with this bogus ICMP traffic preventing legitimate traffic from getting through. I contacted the intermediate site and instructed their admin with regards to what to do to prevent their site from being used in an intermediary in this kind of attack. Unfortunately, there are many unsecured sites on the Internet so this kind of attack is inevitable from time to time.