вставить правильны слова Since Facebook, MySpace or Bebo appeared, they
 became
had become
have become

 a great way for young people 
keeping
kept
to keep

 in touch with friends. There are things,however, you should do to stay safe and protect 
yours
yourself
yourselves

. First, if you 
did not want
do not want
have not wanted

 to use your real name, you may invent a nickname. Also, most sites ask you to provide
 their
them
themselves

 with an email address: use any address to avoid spam or unwanted guests. Feel free to write lots of interesting things in your online profile, but never ever put real house 

address
addressed
addresses
 or 
existance
existed
existing

 phone numbers. In fact, don't give any information that potentially could let strangers know your identity, because on the Internet you never know who 
had looked
is looking
was looking

. If you fail to protect their personal data, you 
put
will put
would put

 your friends indanger in the future. So the general massage is: have fun, but take care.