From The Stargate Omnipedia
A subroutine in the Stargate
system which is believed to allow the gate network to compensate for stellar drift over millions of years. The Stargates' dial-home devices
periodically dial one another automatically and transmit updates regarding Stargate coordinates and system modifications.
The Goa'uld System Lord Baal used this to his advantage, spreading a modified version of Jay Felger's "Avenger" computer virus through the entire Stargate network, leaving all gates inoperative. Earth scientists have theorized that these updates occur only once every several hundred years, but the updates triggered by the Avenger computer virus cast doubt on this theory.
An older version of the Stargates, placed on worlds in distant galaxies by Ancient Seed ships, use a version of correlative updates to maintain real-time communication with Destiny. Rather than periodically dialing one another, these gates have sub-space transmitters that they use to send the ship updates on its status (i.e. whether or not it is available to be dialed) even before Destiny drops out of F.T.L. This update system also allows the Ancient remote to locate other Stargates in range, including the one on board Destiny (in real time, until it goes out of range).
Avenger 2.0 - Carter speculates the Stargate network undergoes automatic correlative updates to compensate for stellar drifting and general program updates. Baal uses the system to spread a modified computer virus and shut down the gate network.
Lost - When he is stranded on a planet with Matt and Chloe, Eli's remote detects when Destiny is and is not in range of the Stargate.
Common Descent - Eli taps into a Stargate's correlative update system to transmit a basic message to Destiny using Morse Code.