Online backup has been around for a while but the idea behind Carbonite is to make it easier, so the user hardly even knows it’s happening.

The first step is to download the Carbonite software from the company’s site and run it. The program asks you to specify the folders you want to back up – My Documents and emails are good places to start – and it then transfers them to its secure servers over the internet. It does this in the background and the software yields to other applications, so you shouldn’t notice much difference while it's copying.

Once Carbonite has made its initial copy, which may take a couple of days if you have lots of data, it continuously monitors the PC and updates the backup with only the files that have changed, which takes much less time. Should the worst happen and you lose data through hardware failure, theft or another calamity, the files can be recovered from any computer that can contact Carbonite’s secure server.

Give it your password and you can download the data to the original computer or to any other. The company's servers are in the eastern US, but does that make them less secure? That shouldn’t be a concern, because everything is scrambled before it leaves the computer, using industrial-grade techniques, and it stays that way all the time it’s on the company's servers.

So how does Carbonite stack up against simply using DVDs or an external hard disk for backup? The online service costs $50 (£25) a year, for an unlimited capacity. Unless you have a very fast broadband link, though, it’s unlikely you’ll be doing a complete file backup onto Carbonite, simply because of the time it takes. You would certainly be able to copy more files, and make a full backup, to an external USB disk.

These disks, including backup software, cost £60-£70 for capacities of 250-500GB and you would expect an external disk to last at least three years. So the costs are similar, but Carbonite has the advantage of offering global access to the data, from any machine with an internet connection, so could prove more convenient.