1. Today's modems are controlled by the old Hayes "AT" command set. In order to dial the phone number 555-1212 using a modem, you simply send the string "ATDT555-1212" to the modem. The "D" following the "AT" means to "Dial", and the "T" means to use "Tone" dialing (rather than "P" for "Pulse" dialing). The command "ATH0" means to hang up the modem. Key point: One of the juvenile tricks people play is to cause people to hang up their own modem. Once the modem connects, it goes into a different mode where it no longer accepts AT commands. However, a user can switch back to the command mode by sending the characters "+++" to the modem. Therefore, if somebody can remotely trick your PC into sending "+++ATH0", then your modem will hang up. One way of doing this is with the ping program that sends and ICMP echo to the victim, which then replies with the same contents. E.g.: ping -p 2b2b2b415448300d victim The most popular exploits for this are spoofed ICMP pings, but it can be exploited in any number of ways. For example, one may include the following in an HTML webpage: <IMG src="http://www.robertgraham.com/images/x.gif?+++ATH0"> From Hacking-Lexicon