"So, if you've accepted me as a friend of a friend, I know your name, your address and your birth date.
"From that, I can go to 192.com and on there I can find out what you do for a living, how much your home is worth - and whether you're likely to be worth burgling.
"I might have already made up my mind because you've posted party pictures on Facebook and I can see what kind of valuables you have in the house - and which rooms they're in. Then you go and tell your Facebook friends how much you're looking forward to going on holiday next Tuesday.
"I can go on to Google Street View and see actual photographs of your home. I can see if you have a burglar alarm, or whether there are any bushes in the garden to hide in. And I can see all the alleyways I can escape down. And, of course, I know you won't be at home.
"Once you accept a stranger into your Facebook account, they can begin what we call social engineering - delicately asking questions to build up information about you,' said Jason Hart, senior vice president of CRYPTOCard Network Security.
"And that can cause havoc. Let's say they got your email address, then they could go to your email account pretending to be you and saying you have forgotten your password.
"Once they have that secret information, the email account will let them in. And once they are in there, they can find lots of sensitive information, such as your Amazon and eBay account history.
"They can then go to those sites pretending to be you and saying you have lost your passwords, and guess what happens then?
"Those sites send the passwords to your email account - the one that they have already conned their way into.
"Crooks who do this usually use the credit card details you have stored there to buy online gift vouchers that can be traded on the internet. It is a form of instant currency.
"Even worse, if you have a PayPal account and have credit in it, your so-called friend could clean it out.
"Effectively, they have become an electronic version of you, they can change all your passwords and begin stealing from you.
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