В интернете нашел полезную короткую заметку про безопасность при использовании соц.сетей. Она мне очень понравилась, привожу ее полностью (на английском):
Guidelines for social networking sites' users
What is important to remember about?
The Internet stores everything! Be careful with sharing information about yourself - whatever you write about yourself or others, erasure of such information and all its made copies from the Internet is very difficult or even impossible.
Be careful with making friends online - just as in real life - people you meet on the Web may not be the ones they claim to be and they may not want to be your friends at all.
Think about what kind of personal information you are placing on the Web. Would you like this information to be available to your employers, teachers, contractors ...?
During registration in a networking service and its use later on, do not enter your full personal data - it's enough to enter only those data which help your real friends to easily find you.
While you sign up for a networking website, try to use other IDs and passwords than those you use for important services such as online banking service.
To increase you security in a social networking service try to use secure passwords and change them periodically. You can build a secure password by mixing different types of characters, i.e. using lowercase and uppercase letters, numbers and special characters. Avoid trivial passwords such as your name, date of birth, your dog's name, etc. Remember that a password today thought to be secure may not be such in the future.
Lack of session encryption between you and a social networking website may at best result in takeover or manipulation of information which you send at a given moment, and at worst - in identification theft, i.e. stealing and using your personal data to achieve benefits.
While you publish photographs with your own image or images of other people, you must be aware that you significantly facilitate identification of yourself and others and you may provide this way much more information than you think you do.
While giving on a social networking site information on another person and publishing that person's photographs, make sure that this person does not object to this publication.
Remember that despite keeping privacy in the networking service, your anonymity is limited and does not exist for the service providers and law enforcement authorities in case of law breach.
Do not forget that not only the social networking site's servers may "know something" about you - you may be sure that persons managing the servers mediating in the connection between you and the networking service may possess some information about you.
If a social networking service allows for an optional use of additional safeguards increasing the quality of your privacy and secrecy of your activities, do not hesitate to use them.
Use the options allowing to limit a circle of people to whom the information about you will be disclosed.
Having in mind your security and the security of others as well as the functionality of the service, do set the sufficient level of your privacy by yourself.