An INVITE of Death is a type of attack on a VoIP-system that involves sending a malformed or otherwise malicious SIP INVITE request to a telephony server, resulting in a crash of that server. Because telephony is usually a critical application, this damage causes significant disruption to the users and poses tremendous acceptance problems with VoIP. These kinds of attacks do not necessarily affect only SIP-based systems; all implementations with vulnerabilities in the VoIP area are affected. The DoS attack can also be transported in other messages than INVITE. For example, in December 2007 there was a report about a vulnerability in the BYE message ("BYE BYE") by using an obsolete header with the name "Also". However, sending INVITE packets is the most popular way of attacking telephony systems. The name is a reference to the ping of death attack that caused serious trouble in 1995–1997.