A former Unix system admin at Medco Health Solutions, a big US drugs prescription management firm, has admitted to planting malicious code that would have destroyed massive amounts of critical patient information.

Yung-Hsun Lin pleaded guilty in US District Court in Newark, New Jersey on Wednesday over the charge of transmitting code that would cause damage to a protected computer in excess of $5,000. The crime carries a maximum penalty of 10 years in prison and a $250,000 fine.

Lin had allegedly planted a "logic bomb" computer virus on Medco's systems in October 2003 over concerns he would lose his job after the company was spun off from Merck & Co that year. The code was designed to delete nearly all data from 70 servers, which included patient files listing adverse affects to particular drugs and billing information.

When the code failed to launch a year after he had authored it, Lin reprogrammed the virus to go off on his next birthday (April 23, 2005) despite him surviving the lay-offs, according to authorities. This time his plan was foiled by Medco investigators who detected the code before it was activated. He admitted his actions to the investigators, who tape recorded him, Assistant Attorney Erez Liebermann said. Medco said it cost the company between $70,000 and $120,000 to fix the code.

Lin's sentencing is scheduled on January 8. ®

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