Espionage is a part of intelligence activity, which is also concerned with analysis of diplomatic reports, newspapers, periodicals, technical publications, commercial statistics, and radio and television broadcasts. In the last fifty years espionage activity has been greatly supplemented by technological advances, especially in the areas of radio signal interception and high-altitude photography. Surveillance with high-technology equipment on the ground or from high-altitude planes and satellites has become an important espionage technique (see Cuban Missile Crisis). The development of the Internet has created opportunities for espionage through hacking into foreign government and private computers, through electronic surveillance of Internet and network traffic, and through the use of trojan horses, key loggers, and such computer programs. Code making and code breaking (see cryptography) have become computerized and very effective. The threat of foreign espionage is used as an excuse for internal suppression and the suspension of civil rights in many countries. Espionage is a very important part of guerrilla warfare and counterinsurgency. The defensive side of intelligence activity, i.e., preventing another nation from gaining such information, is known as counterespionage. Under international law, intelligence activities are not illegal; however, every nation has laws against espionage conducted against it.