Until 2365, within the Federation it was widely believed that the Iconians were a myth. They were widely known in archaeological circles as ancient "demons of air and darkness" who were able to appear at will anywhere, travelling without benefit of spacecraft. On Stardate 42597.17 Captain Donald Varley of the Galaxy class USS Yamato was given an artefact thought to be Iconian when visiting an archaeological site. He was able to translate symbols on the artefact and after correcting for 200,000 years of stellar drift he was able to determine that the location of Iconia itself was in the Romulan Neutral Zone, close to Romulan space.
Varley proceeded into the Zone and encountered an active piece of Iconian technology around Stardate 42607.95. The device scanned his ship, whereupon the Yamato began to suffer various computer malfunctions. Immobilized, Varley called Captain Picard for assistance. Unfortunately, shortly after Picard arrived the Yamato began an emergency dump of its antimatter stocks. The dump was then halted and the containment fields dropped while sufficient antimatter was still present to cause a catastrophic explosion.
The Enterprise itself then began to experience similar computer malfunctions. It was determined that the Yamato had contracted a form of computer virus from the Iconian probe, which had communicated itself to the Enterprise via the communications system when the ship had transmitted its log entries. The Enterprise was able to destroy another probe before it could cause further contamination.
On Iconia itself Picard discovered the source of many of the legends concerning the Iconians; the Iconian gateway. The gate appeared as an oblong panel in the air with various destinations displayed in it. To reach a destination one simply stepped through at the proper time, crossing light years in a moment.
Picard was able to use the gateway to escape the planet after setting the generator equipment to self destruct so as to prevent it from falling into Romulan hands. The ship was able to clear out the Iconian program by conducting a complete shutdown and reboot of all computer systems and escaped from the area without further incident.1
A second Iconian gateway was discovered in the Gamma Quadrant by a force of rebel Jem'Hadar, who planned to use it to break away from the Founders and overthrow the Dominion. A joint Federation / Dominion assault force raided the location of the gate, which was protected by neutronium armour impenetrable to conventional weapons and a dampening field which rendered phasers inoperable. They joint force were able to fight their way to the gate and plant explosives to destroy it.
To date no further trace of functional Iconian technology has been discovered.2