The former employee of a US pharmaceutical company who was charged with computer intrusion to bring down the company's operations for several days in February has pleaded guilty to the charges and is facing up to 10 years in prison, Computer World reported.

Jason Cornish, 37, logged into his former employer Shionogi's network from a public Internet connection at a McDonald's in Smyrna, Georgia, and deleted 88 virtual servers from 15 physical hosts through VMware vSphere console, according to court filings reviewed by Computer World.

Systems affected ran email, order tracking, financial and other services for the US subsidiary of the Japanese drug maker Shionogi. Cost of the attack to the Florham Park, New Jersey-based company was determined to be US$800,000.

The US Department of Justice wrote in its court documents: "The Feb. 3 attack effectively froze Shionogi's operations for a number of days, leaving company employees unable to ship product, to cut checks, or even to communicate via e-mail."

In July 2010, Cornish got into a dispute with his management at Shionogi and resigned, but kept working for the company as a consultant until getting laid off about two months later. According to Computer World, the company "did a bad job of revoking passwords to the network", following a round of lay-offs that Cornish was a part of.

Cornish reportedly installed the vSphere console he used to attack Shionogi's network a few weeks before he committed the attack.

He is expected to be sentenced on 10 November.