Whenever you are involved in any online activity you must allow be aware that threats exist and that you should take reasonable precautions against these risks. It may not be possible to avoid every potential danger but if you realize that there are threats out there then will mean that you use the social networking web sites responsibly, for example, you may decide not to enter too much personal information in case this information gets out, for example, you would not put an advert in a newspaper to say that you will be on holiday abroad fro two weeks and that your house will be empty during that time.
You should also be careful about who you allow to be your online friends and contacts because there is no way, other than meeting someone face to face, that you really know who the other person is. It could be that one of your contacts is using the social networking site for criminal activity, such as identity theft, where one person tries to steal the identity of another for some sort of benefit.
You must also be careful about believing everything that you read on a social networking site. It could be the one of your contacts uses your email address to send you a fake email from your bank asking you to reply and to include personal details including your account name and password. This contact would not have been able to carry out this scam, known as phishing, if they did not have your email address.
You should also be very careful if one of your contacts, who you do not know personally, asks you to meet up with them. It may be that the meeting will be fine, however, it would pay to be very careful in a situation like this and if you did agree to meet with any of your social networking contacts that you make sure that more than one person is going to be there and that you will be going with some friends that you already know.