Dr. Jay Felger had created Avenger, a computer program he had named for a comic book hero who wore green tights and a purple cape. Faced with losing his job as a research scientist at the SGC, Felger collaborated with Carter and his research assistant, Chloe, to revisit and revise the unproven program. The updated program, Avenger 2.0, was a computer virus designed to scramble a DHD's established coordinates for a specific stargate so that the gate symbols and coordinates would no longer correspond, rendering the target gate useless to the Goa'uld, and providing a tactical advantage to Earth.
P5S-117, a planet in Ba'al's domain, was selected as the target gate to test the virus, however, within hours of the test, the new coordinate system spread to all the DHDs, and the entire stargate network shut down. Twelve SG teams were stranded off-world, and only Earth's stargate was capable of establishing an outgoing wormhole because it relies on a dialing computer rather than a DHD. Felger and Carter theorized that Avenger had triggered an automatic correlative update, causing the DHDs themselves to spread the new coordinate system, and the virus was now blocking attempts to upload new dialing programs into the DHDs. They determined that the problem could only be corrected by going to P5S-117 and physically removing the control crystal from the DHD which would eliminate the virus source, reboot the system, and trigger another correlative update.
Once on the planet, however, they discovered that Ba'al had tampered with the virus to use it to his advantage, using the automatic update program to disseminate it from gate to gate, and that it was the modification, not Avenger, that had shut down the gate network. Felger was able to alter an anti-virus program to specifically target and neutralize the modified version of Avenger, which successfully brought the gate system back online.
Cross Reference: Automatic Correlative Update, Ba'al, Chloe, DHD, Jay Felger, P3C-249, P3L-997, P5S-117, Stargate
Episode Reference: Avenger 2.0