A computer program created by the Wraith and implanted into the computer systems of the Daedalus through a highly compressed data burst before the ship could depart from the Pegasus Galaxy, it took several weeks to decompress and become a threat. Upon the ship's return to Wraith territory, the virus activated. Designed to pilot the ship into enemy hands, the Wraith would have not only the crew, but the intergalactic hyperdrive technology and the coordinates to a new feeding ground in the Milky Way.
Since it is an Artificial Intelligence, the virus is capable of ascertaining threats and developing appropriate solutions. When it realized the inhabitants of the Daedalus were a threat to its objectives it steered the ship toward the corona of the nearest star, intent on killing everyone on board.
The virus seems to be able to copy itself into the ship's various computer systems, including the F-302 fighter-interceptor's on the ship's hangar deck. It was eliminated by a full system shut down and restore from back-ups after all of its hiding places were destroyed. (SGA: "The Intruder")