Signals Intelligence in Modern History - 1990s

1990s

Terrorism from foreign groups became an increasingly major concern, as with the 1992 al-Qaeda attack in Yemen, the 1993 truck bombing of the World Trade Center, 1995 (Saudi communications center) and 1996 (Khobar Towers) in Saudi Arabia, and the 1998 bombings of the US embassies in Dar es Salaam, Tanzania and Nairobi, Kenya. Third world and non-national groups, with modern communications technology, in many ways are a harder SIGINT target than a nation, such as Russia or China, that sends out large amounts of traffic. According to the retired Commandant of the US Marines, Alfred M. Gray, Jr., some of the significant concerns of these targets are:

• Inherently low probability of intercept/detection (LPI/LPD) because off-the-shelf radios can be frequency agile, spread spectrum, and transmit in bursts.
• Additional frequencies, not normally monitored, can be used. These include citizens band, marine (MF, HF, VHF) bands, and higher frequencies for short-range communications
• Extensive use of telephones, almost always digital. Cellular and satellite telephones, while wireless, are challenging to intercept, as is Voice over IP (VoIP)
• Commercial strong encryption for voice and data
• "Extremely wide variety and complexity of potential targets, creating a "needle in the haystack" problem"