An employee at US banking group UBS has been accused of crippling the organisation he worked for by releasing a virus onto its internal network.

Roger Duronio – who denies the claims - was said to have been unhappy at receiving an annual bonus of only $32,000 on top of his $125,000 salary, which caused the former programmer to release a “logic bomb” that shut down 2,000 computers at the bank’s stockbroking arm, PaineWebber.

His actions are believed to have been motivated by his desire to make up the loss by making a "put" options bet that the share price would fall, then driving the price down by instigating the security scare.

The company alleged in a New Jersey court that this stopped 17,000 brokers from around the world from being able to trade shares for the whole of the day of the attack, 4 March 2002.

Losses for the repairs alone were estimated at $3.1 million, with an unknown amount from the inability to trade. Duronio’s alleged plan failed – the share price did not fall.

UBS is reported by to have asked for the case to be heard in private, claiming that the security sensitivity of some of the evidence might compromise the company’s wider security.

In his defence, the accused’s lawyers have pointed to security flaws said to have affected the company’s networks during the period before the attacks, and which could have contributed to the disastrous events of 4 March.

The case continues.