A former Unix system administrator at Medco Health Solutions' New Jersey office has pleaded guilty in the US federal court to attempting to sabotage critical data, including individual prescription drug data, on more than 70 servers.

Yung-Hsun Lin, also known as Andy Lin, 51, of New Jersey in the US, is scheduled to be sentenced on January 8. He faces a maximum sentence of 10 years and a fine of US$250,000.

Lin was one of several systems administrators at Medco who feared they would get laid off when their company was spun off from drug maker Merck in 2003, according to a statement released by federal law enforcement authorities. Apparently angered by the prospect of losing his job, Lin on October 2, 2003, created a "logic bomb" by modifying existing computer code and inserting new code into Medco's servers.

The bomb was originally set to go off on April 23, 2004, on Lin's birthday. When it failed to deploy because of a programming error, Lin reset the logic bomb to deploy on April 23, 2005, despite the fact that he had not been laid off as feared. The bomb was discovered and neutralised in early January 2005, after it was discovered by a Medco computer systems administrator investigating a system error.

Had it gone off as scheduled, the malicious code would have wiped out data stored on 70 servers. Among the databases that would have been affected was a critical one that maintained patient-specific drug interaction information that pharmacists use to determine whether conflicts exist among an individual's prescribed drugs.

Also affected would have been information on clinical analyses, rebate applications, billing, new prescription call-ins from doctors, coverage determination applications and employee payroll data.

During a plea hearing at the US District Court in Newark, New Jersey, Lin pleaded guilty to one count of transmitting computer code with the intent of causing damage of around US$5,000.

The case is one of the most egregious examples yet of attempted computer sabotage by an insider, Assistant US Attorney Erez Liebermann told Computerworld. Unlike most malicious logic bombs, which are designed to disrupt operations or inflict financial damage, Lin's malicious code could have affected "life and limb", Liebermann said.

The incident highlights a danger posed to companies by disgruntled employees, Liebermann said. "Some event triggers unhappiness on the part of the employee, which is why we have counselled companies to be extra-vigilant about hiring and firing staff." Also, companies should take care when handing out incentives and bonuses, he said.

Liebermann pointed to the case of Roger Duronio, a systems administrator at UBS PaineWebber. In July 2006, Duronio was found guilty of planting a logic bomb that affected around 1,000 of PaineWebber's US computers, costing the company some US$3 million in damages. Duronio, who was sentenced to more than eight years in prison, planted the bomb because he was unhappy with his pay and bonuses.

Tracking down such individuals can be challenging because they often hide their tracks, Liebermann said. In both the Duronio incident and in Lin's case the malicious code was designed to wipe itself out of existence after the attack, he said.