PC security Have you heard the one about the Scotland Yard staff who couldn't resist sharing the odd tale on Facebook? Given their line of work, you'd think they'd practise a bit of caution. Stories like these are manna to the press, you know. They're also of interest to another none-too-popular group: hackers.

It's not just ironic tittle-tattle you have to watch out for: information of all types can come in useful. It's no small coincidence that thrillers and detective novels often centre on what someone knows or what they have in their possession.

Take William Boyd's Ordinary Thunderstorms. The main character must conceal his possession of damning information that's been inadvertently passed on to him; simultaneously, he must leave no trace of his whereabouts and keep his identity hidden. Without the accoutrements that make up his identity, he's able to assume someone else's identity and effectively disappear.

But ID theft isn't restricted to fiction. Tales of people exploiting each other turn up time and again. I recently caught a documentary where a seemingly overprotective boyfriend wouldn't let his better half open her post. Little wonder: he'd racked up £14,000 of debt in her name, and the final demands were coming in fast.

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While few of us have gone through the discomfort and inconvenience of having someone assume our identity, tales of how nuggets of information have fallen into the wrong hands and been exploited are worryingly common.

It's not even necessarily malicious. My grandfather unwittingly paid for someone else's gym membership for months - not because the chap had posed as him, but because the bank had taken the payment from the wrong customer's account. Electronic communications and our faith in the system can make mugs of us all.

As this issue's in-depth look at the latest web threats and security issues shows, the details we knowingly share with friends and associates are just as likely to leave us open to exploitation as the sensitive information that phishers make concerted efforts to acquire. Try Googling your own name. You'll find web crawlers have acquired a worrying amount of detail about you.

Problems with passwords

The slightest crumbs of information, when gathered together, can be used for all sorts of purposes. Hackers recently exploited the common, but potentially dangerous habit of reusing the same password for webmail, Facebook, eBay, Flickr and other sites. Using the various information stored at these sites, they can rapidly assemble a picture of the person behind the password, complete with their age, occupation, date of birth, address and so on. Enough, in other words, to steal their identity or access some of their more secure accounts.

Next time you sign up to an online service and are asked for details about yourself, consider what those details reveal about you and where it may end up. Passwords are there to protect us. It's time to start using them wisely.

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