Showing Chinese sweatshop workers slumped over their desks with exhaustion, it is an image that Microsoft won't want the world to see.

Employed for gruelling 15-hour shifts, in appalling conditions and 86f heat, many fall asleep on their stations during their meagre ten-minute breaks.

For as little as 34p an hour, the men and women work six or seven days a week, making computer mice and web cams for the American multinational computer company.

Worn out: Some of the workers making computer accessories for Microsoft at a Chinese factory

This photo and others like it were smuggled out of the KYE Systems factory at Dongguan, China, as part of a three-year investigation by the National Labour Committee, a human rights organisation which campaigns for workers across the globe.

The mostly female workers, aged 18 to 25, work from 7.45am to 10.55pm, sometimes with 1,000 workers crammed into one 105ft by 105ft room.

They are not allowed to talk or listen to music, are forced to eat substandard meals from the factory cafeterias, have no bathroom breaks during their shifts and must clean the toilets as discipline, according to the NLC.

The workers also sleep on site, in factory dormitories, with 14 workers to a room.

They must buy their own mattresses and bedding, or else sleep on 28in-wide plywood boards. They 'shower' with a sponge and a bucket.

And many of the workers, because they are young women, are regularly sexually harassed, the NLC claimed.

The organisation said that one worker was even fined for losing his finger while operating a hole punch press.

Microsoft is not the only company to outsource manufacturing to KYE, but it accounts for about 30 per cent of the factory's work, the NLC said. Companies such as Hewlett-Packard, Samsung, Foxconn, Acer, Logitech and Asus also use KYE Systems.

Microsoft, which exports much of the hardware made at the factory to America, Europe and Japan, said that it is taking the claims seriously and has begun an investigation.

One employee told the NLC: 'We are like prisoners. It seems like we live only to work - we do not work to live. We do not live a life, only work.'

The NLC's report included an account from one worker whose job consisted entirely of sticking selfadhesive rubber feet to the bottom of Microsoft computer mice.

But the monotony of sitting or standing for 12 hours, applying foot after foot to mouse after mouse, was not the worst of the worker's testimony.

It was the militaristic management and sleep deprivation that affected the worker most. 'I know I can choose not to work overtime, but if I don't work overtime then I am stuck with only 770 Chinese yuan (£72.77p) per month in basic wages,' the worker said.

'This is not nearly enough to support a family. My parents are farmers without jobs.

They also do not have pensions.

'I also need to worry about getting married, which requires a lot of money. Therefore, I still push myself to continue working in spite of my exhaustion.

'When I finish my four hours of overtime, I'm extremely tired. At that time, even if someone offered me an extravagant dinner, I'd probably refuse. I just want to sleep.'

Charles Kernaghan, executive director of the NLC, said: 'It sounded like torture - the frantic pace on the assembly line, same motion over and over for the 12 hours or more of work they did.'

Microsoft said it was committed to the 'fair treatment and safety of workers'. A spokesman added: 'We are aware of the NLC report and we have commenced an investigation.

'We take these claims seriously and we will take appropriate remedial measures in regard to any findings of misconduct.'