I'm getting adverts (on BCG and elsewhere) for something called Xtra-PC that promises to completely rejuvenate any old computer and make it run like an Olympic sprinter.

It's a USB thumb drive and comes in a variety of specifications, the most expensive being about £80.

All you do is plug it into your computer and boot up from that thumb drive. Voila! Brand-new performance!

It's a great idea but a little investigation reveals that what you get for your money is, in fact, a SanDisk Cruzer Glide USB stick with SanDisk's logos covered by replacement stickers saying "Xtra-PC".

Loaded onto the USB stick is a LINUX operating system that is available absolutely free all over the Internet.

The USB stick itself is available on eBay and elsewhere from prices as low as £9.99

I am certainly not a computer "expert" but I'm capable of making one of these for myself at £9.99 rather than paying £80 for the bloody thing!