Logging in from a McDonald's restaurant, a former employee of a US pharmaceutical company was able to wipe out most of the company's computer infrastructure earlier this year.

Jason Cornish, 37, formerly an IT staffer at a subsidiary of Japanese drug maker Shionogi, pleaded guilty Tuesday to computer intrusion charges in connection with the attack on February 3, 2011. He wiped out 15 VMware host systems that were running email, order tracking, financial and other services for the company.

"The 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 email," the Department of Justice said in court filings. Total cost to Shionogi was around $800,000 (£488,000).

Cornish had resigned from the company in July 2010 after getting into a dispute with management, but he had been kept on as a consultant for two more months. Then, in September 2010, the drug maker laid off Cornish and other employees.

However, it appears that it did a bad job of revoking passwords to the network. One employee, who was Cornish's friend and former boss, allegedly refused to hand over network passwords to company officials and eventually was fired because of this.

Using a Shionogi account, Cornish was able to log into the company's network from a public McDonald's Internet connection in February and fire up a vSphere VMware management console that he'd secretly installed on the company's network a few weeks earlier. Using vSphere, he deleted 88 company servers from the VMware host systems, one by one.

Cornish faces a maximum of 10 years in prison when he's sentenced on November 10. He could not be reached for comment. Shionogi did not return messages seeking a response.