Arguing his appeal against his jail term of two years and six months, his lawyer Raymond Lye told the High Court on Friday that Neo's passwords had been written on a piece of paper near the computer making it possible for anyone to log on.

Dismissing the this imposter theory, Deputy Public Prosecutor Christopher Ong said it was 'something more from the Mission Impossible movies than from reality'.

For it to work would require up to three imposters and precise timing, he pointed out.

Neo's alibi, backed by minute-by-minute sequence to show that he was not in his office when the hoaxes were sent, smacked of fabrication, DPP Ong said.

His arguments convinced Justice Choo Han Teck to dismiss Neo's appeal against the sentence imposed by a district court in Jan.

However, the appeal by prosecution for the High Court to increase Neo's jail term also failed.

Neo, 39, was found guilty on three charges of posting bomb hoax messages on the websites of the Prime Minister's Office and the Ministry of Home Affairs in 2005.

He was a jailed a year and three months on each charge under the United Nations (Anti-Terrorism Measures) Regulations, by District Judge Bala Reddy, who ordered the jail term to run together.

Neo, who was then a senior manager with the National Environment Agency's North-East Regional Office in Sin Ming Drive, had e-mailed a Home Affairs Ministry website about 'rumours of possible suicide bomb in Bedok area in 2 to 3 weeks time' on Oct 18 2005.

Later that day, he referred to a 'possible bomb attack in Singapore in an event with water activities involving head of state, ministers etc within a month.'

The next day, he sent a message to the PMO Feedback Unit about 'a plot to conduct suicide bomb attack against PM, Ministers and MPs in a major event in Bedok Reservoir area in the coming weeks'.

All the messages were sent using fake Muslim names.

Earlier, the court heard from Neo's lawyer that the evidence used to convict Neo was purely circumstantial,

He also disputed the prosecution's contention that Neo had sent the bomb hoaxes because he was unhappy over losing a promotion to a Muslim.

'He would have been incredibly dumb to use his office computer to post the bomb hoaxes,' said Mr Lye.

However, DPP Ong said that Neo had sent the messages anonymously and may have not realised that these could be traced.

Neo, who has been out on bail, began his sentence on Friday.