The Iconian software transmission was an information transfer developed by the ancient Iconian civilization. The software used a small probe that uploaded a program into the target's computer system. Once there, the program began rewriting the software of the destination computer. If the recipient was not Iconian, it began to cause malfunctions, eventually reaching catastrophic systems failure. The purpose of this transmission was never discovered.
In 2365, the USS Yamato discovered the Iconian homeworld in the Romulan Neutral Zone and was subsequently infected by the Iconian probe. The Yamato was later destroyed by the program when it caused an uncontrolled release of antimatter into the Yamato's warp core. The program spread to both the USS Enterprise-D and the IRW Haakona when they downloaded the Yamato's logs. Enterprise Chief Engineer Geordi La Forge discovered that the program could be purged by shutting down all ship's systems, erasing the infected areas, and then rebooting from the computer core's protected memory. This technique was discovered when Lieutenant Commander Data, an android who had also been infected by the program, appeared to die, but awakened moments later as his systems had automatically restored his programming to normal. (TNG: "Contagion")