Sitting at a desk for hours working at a computer may earn you brownie points with your boss, but doctors are now warning it could also kill you.

While most of us are aware of the risks of sore eyes or a stiff neck, it now appears that lack of movement could make millions of workers vulnerable to a new health risk - 'e-thrombosis'.

It's a type of deep vein thrombosis (DVT) and is the same condition known to affect airline passengers - several healthy passengers have died after trips abroad.

Thrombosis or blood clots can form when people are sitting for long periods in one place, especially where the legs may be cramped or circulation restricted.

Dr Beverley Hunt, medical director for thrombosis charity Lifeblood, says: "Sitting for very long periods in an office has never been considered a risk before but it is because immobility is a key factor in causing thrombosis."

Hunt says thrombosis is "a hidden, silent epidemic". Each year up to one in every 1,000 people in the UK is affected by a blood clot in the veins, and 60,000 a year die from it.

"People are moving around less and it's not uncommon for someone to spend hours sitting at work and then go home and sit and watch television or play computer games," she says.

"This adds up to huge stretches of immobility and adds to the risk of a clot forming."

Dr John Scurr, a consultant vascular surgeon at London's Lister Hospital, said: "In the last nine months I've seen around seven cases of people suffering from this, some of them are City brokers or lawyers who think nothing of 12 to 14 hours a day working on a computer."

You should consult a doctor if you have any of the following symptoms: A swelling of the calf; a pain in the calf which is noticeable and becomes worse when standing or walking;chest pain and shortness of breath. This needs emergency treatment.

DVT is highly treatable and anticoagulant medicines are the most common treatment. Always take a tea break away from the computer, and avoid lunching at your desk. Instead walk around and stretch your legs. Cardiovascular exercise not only lowers the blood pressure, but also reduces the risk of clots building up in the first place. Drink plenty of fluid, at least eight glasses a day, to avoid dehydration, one of the risk factors involved in DVT.

Walking around only five to 10 minutes each hour could substantially reduce your risk of e-thrombosis.