Imagine if the Home Office decided that the best way to fight terrorism was to ban curtains.

"Hang on!" we'd say. "That means Creepy Dave across the road will be able to see me in my underpants!"

The Home Office would nod sagely. "That's true, but you know who else has curtains? Terrorists! Terrorists and gangsters! So it's curtains for curtains!"

The Home Office hasn't banned curtains just yet, but it's getting closer. Over the weekend we discovered that incoming legislation means that the police will be able to install spyware on anybody's PC without asking the courts for permission. Inevitably it's to fight terrorism, organised crime and Gary Glitter.

If the police want to search your house, they need a warrant; if they can't produce evidence that one's necessary, they don't get it. That seems perfectly sensible to us. However, under the new rules police will be able to search your electronic property without a warrant. All they need to do is get the go-ahead from a senior officer who "believes" it's necessary.

That's terrifying, because there's a long and rather depressing history of computer powers being misused. We know that the Police National Computer is used to check up on cops' estranged partners or their daughters' boyfriends, or to give tabloids information they shouldn't have. And we know that the anti-terrorism powers introduced under the Regulation of Investigatory Powers Act have been used to spy on parents of schoolchildren and owners of crapping dogs.

Until somebody invents a real Robocop, all police officers are people - and that means that some of them will make bad decisions, and that a tiny minority of them are just bad. The police are there to protect us from the dangerous few - and warrants and other safeguards are there to protect us from a dangerous few police officers.

Without safeguards it's not a question of if the new snooping powers will be misused; it's a question of when, and what damage will be done.

Should the police have the tools they need to fight crime? Absolutely. Should they have the power to do whatever they want, without having to answer to anybody? Absolutely not.

Your PC, like your home, is private property, and the privacy of your PC is like the curtains over your windows. You don't have curtains because you're up to no good. You have them to prevent people from staring through your windows for no good reason.