Are you advertising your home to burglars?
Dave Turner, a 22-year-old intern from London, was excited about going to Glastonbury this year. He updated his Facebook status when he bought the tickets and again when he was about to leave.
He even joined a group on the site for people who were going. He says: "I put a post up because I wanted to know what to take with me."
The festival was everything he had hoped for, but the experience was ruined because when he returned he found his home ransacked. He says: "They were in here a while to take as much as they did: they must have known I was away.
I mentioned it to the police, and they asked if I'd put anything up on social networking sites. It was the first time I'd thought of it."
Dave had listed his address, the fact he was single, and posted enough information for burglars to know he would be away for the duration of the festival. He had essentially advertised his home to criminals.
Around 20 million people in the UK have taken to social media like Facebook, MySpace, Bebo and Twitter. Users think of it as talking to friends, so they don't consider the dangers of who else may be watching.
Tony Neate, managing director of government site GetSafeOnline.org, says: "We are much more open about ourselves and our lives online, and sites provide rich pickings for criminals."
But burglary is not the only risk. Criminals are constantly thinking of new ways to take your money.
In September there were reports that hackers had begun breaking into Facebook accounts and sending messages to all the users' friends saying they had been mugged and left stranded on holiday, and asking for money to be wired to an account.
Using social networking sites may also make you vulnerable to identity theft. Fraudsters may well be able to see your personal information in something like Facebook, which reveals details of your name, address, contact numbers, education and employer, which will get them a good way down the road to stealing your identity.
If you include things like family information and the names of your pets, you have also given them helpful clues to crack more complex identity protection codes like secret questions and passwords.
Fraudsters can also pull information from a host of other sites, including CVs you may have posted on recruitment websites, and wish lists you have set up with retailers.
How to protect yourself
First of all, it pays to be cagey about what you post. A survey by Nextadvisor.com found 8% of people list all their personal details on their profile, which is especially dangerous.
Never include details like your address, don't post photos of your home, and think carefully before disclosing details about your life including any holidays or your working patterns.
You can hide things you post on a site like Facebook by protecting your profile. This means your personal information like your contact details and address will be hidden from everyone except your friends.
However, this won't entirely protect you, as people will still be able to find out basic information like your date of birth, home town, education and workplace simply by sending you a friend request. If you respond by asking who they are, you automatically allow them to see your basic information. Also, be careful about who you accept as a friend.
Think about the extra details that appear on your site too. So, for example, if you have left your date of birth or your surname off your profile, but it forms part of your email address, you're not very well hidden.
It's also worth checking what is already online about you. There are a growing number of companies keen to sell you services, like Garlik (garlik.com), which will check for your data online. There are also some free services, such as 123people.co.uk, which brings together the details of everyone with your name online.
It also has a feature called a Tag cloud, which lists the words most associated with you, which may help you find where this information is coming from, so you can close down the offending account or delete the information.
In the end it comes down to whether you're happy with the precautions you've taken to protect yourself against cybercrime. Dave didn't want to take any chances. He closed down his Facebook and Twitter accounts, and says: "I don't know if it was Facebook or just bad luck, but it has really put me off putting information onto a website at all."