Thomas Roxborough ran a company called Acquisition Technologies. The company best programmer was David Gavilan (with Lucien Cross as a close second, but I disgress). Dunkelzahn was a shareholder of Acquisition Technologies. He tried to have Gavilan quitting Acquisitech and joining Gossamer Threads, a Dunkelzahn-controlled corporation. This led Roxborough to start a corporate war against Gossamer Threads. He ordered
Acquisitech engineers, including Gavilan, designed a virus to destroy Gossamer Threads network. They tested the virus on a company called Effexx Studios. The virus successfully destroyed Effexx system, and then proceeded to destroy Internet.
As the Crash started, Dunkelzahn met Gavilan to offer him a position at Gossamer Threads. He read his mind and learned about the Virus design. So he suggested him to join Echo Mirage Team Two and try to redeem himself.
That is, as far as the story told in the novel Clockwork Asylum is true.
David Gavilan was the lead programmer of Echo Mirage as "Major David Gavilan". IMO, it suggests Gavilan served in the armed forces for some time before joining Acquisition Technologies (as it is unlikely a civilian in the emergency of fighting the Crash would get a Major rank). And according to Corporate Guide, Gavilan resurfaced at Acquisition Technologies' investigative research division after the Crash.