The Iconian probe scans the USS Yamato
An Iconian probe was a spherical blue orb with energy tendrils arcing at random and was employed by the ancient, powerful and extinct Iconian race to download an operating system into an enemy ship's computer core thereby causing the vessel and its systems to malfunction and possibly suffer catastrophic consequences. Once the ground-based computer detected an incoming vessel into orbit of Iconia, an automated sequence would begin launching one probe per vessel. The probes were housed in a launch bay in the planet's surface. If many were released at once and the egress door failed to open, the resultant detonation would destroy the facility.
A probe affected the USS Yamato on stardate 42592.72 causing a malfunction in the ship's dilithium seals, resulting in the release of matter and antimatter causing the vessel to explode killing all hands aboard. Upon achieving a standard orbit of Iconia several days later, another probe was launched at the USS Enterprise-D, which was destroyed before any systems could be affected. However, the Enterprise-D previously downloaded the Yamato's logs, which contained the Iconian program, thereby "infecting" the Enterprise with the same program that destroyed the Yamato. The data "infection" was later removed. Another probe was launched at the Romulan vessel Haakona. It was destroyed before it could upload any information. However, it, too, downloaded the Yamato's logs and received the program. The crew of the Enterprise were able to aid the Romulans in removing the data before it could be destroyed as well. (TNG: "Contagion")