Some websites can cause the unwary visitor unwarranted suffering and offence. Take, for example, the National Heart, Lung and Blood Institute at http:hlbisupport.combmi. Here you are invited to key in how much you weigh and how tall you are, and within seconds you are told if you are at your optimum weight. I made the mistake of putting the program through its paces and I confess it came as a cruel blow to discover that in order to avoid the stigma of being overweight, I must lose six pounds or, alternatively, grow two inches taller.

Needless to say, the internet - the ultimate self-help manual - is packed with advice on how to get thin. Ten minutes with Google will turn up everything from the British Heart guidelines (www.bhfactive.org.uk) to those insanely irresponsible sites, pitched at adolescent girls, that promote bulimia as a lifestyle choice. The message, however, is always the same: the only way to lose weight is to burn off more calories than you consume.

That’s easier said than done as you’ll soon discover if you visit sites such as http:msnbc.commodulesquizzes caloriecalc.asp where you can calculate how many calories you expend when engaged in various activities.

It makes for uncomfortable - and frankly implausible - reading. For instance, “Having sex (moderate)” for 15 minutes burns off a disappointing 23 calories, which means it’s only marginally better for you than vegging out in front of the telly for an hour (70 calories) - still, it’s a good reason for staying up to watch Newsnight. A frenetic hour racing around the web or a fraught session at the word processor consumes a paltry 128 calories. So after this exhaustive research online (384 calories of it) I’ve reluctantly arrived at the conclusion that losing weight will necessitate doing something a bit more strenuous than pecking at a keyboard and wobbling a mouse.

One compromise would be to punctuate lazy sessions at the computer with short bursts of physical activity. Plenty of websites offer exercises aimed specifically at computer users who would like to get fit but are naturally reluctant to move too far from the VDU. Many are animated so you can see in real time exactly what you should be doing. I have dutifully bookmarked several of these sites. And you guessed it in one - despite the best of intentions, I have never revisited any of them.

That’s what makes Stretch Break such a potentially useful application.

According to the information at www.paratec.com, once you’ve loaded it on to your hard disk, not only does it provide you with a range of modest routines you can do at or near your desk, but, far more importantly, it also provides an on-screen prompt, so every 30 minutes you are reminded to exercise. I’m going to take advantage of the free 10-day evaluation offer and obtain a copy of the program from http:downloads. zdnet.co.uk. If, after the trial period, it hasn’t helped me to improve my weight-height ratio, I’ll have to take the alternative approach and see what’s available at www.growtaller.com

The risk of ending up looking like Mr Blobby is only one of a long list of health hazards that face those of us who spend too much of our time at the keyboard. For confirmation of this, visit ROSPA’s site (www.rospa.org.uk) and you will find that in one year, 150 people in the UK ended up in hospital as a direct result of computer-related accidents. If you want something else to keep you awake at night, search the net using the keywords “computer” and “deep vein thrombosis” - if you believe everything you read, you won’t risk sending an email without first donning your elasticated stockings. Dare to investigate the possible adverse effects of Pulsed Electro-magnetic Radiation - the waves that are emitted by cathode tubes - and you will quickly become convinced that the only safe location for your VDU is in a lead-lined pit at the bottom of the garden.

And if that weren’t enough, computer users really should worry about Repetitive Strain Injury. It’s a condition I have taken seriously ever since I ignored a series of twinges in my right arm and ended up spending a fortnight unable to click a mouse without at the same time emitting heart-rending squeaks of pain. Unlike chronic sufferers whose lives are ruined by RSI, I was eventually able to cure myself but only by applying lashings of Algipan and wallowing shamelessly in self pity: “why, oh why has this happened to me?” I’d grizzle to anyone foolish enough to come within earshot.

The answer was obvious. I’d failed to follow the simple guidelines on how to sit correctly in relation to the keyboard, the screen, and the mouse.

These guidelines can be found at www.hse.gov.uk and countless other sites which teachers should encourage their pupils to visit. Better still, they should check out the BBC’s GCSE Bitesize where the dangers of RSI are sensibly included in lessons on the broader implications of ICT.

Because children become so easily engrossed by activities involving the computer and their muscles are still developing, they are particularly susceptible to RSI. And, of course, if the government’s ambitious plans for e-learning come to fruition, children will spend more of their time at school using new technology and thus will be at even greater risk. Teachers must either make a concerted effort to educate them on how best to avoid the condition - or be prepared to devote a substantial proportion of their ICT budget to stocking up on Algipan.