Data breaches such as occurred this week with Yahoo, which shockingly did not even encrypt the data of its users often lead to even more scams through the use of the email addresses of the hacked individuals to send out phishing emails to unsuspecting victims who see an email from a trusted source that may contain a link that they click on to and unwittingly download malware such as keystroke logging programs that can steal all of the information off of your computer, such as your Social Security number, passwords, credit card numbers and more. The risk of these types of phishing scams always increases following a large data breach such as the recent Yahoo, Formspring and LinkedIn data breaches.
Always check with any website or company that will have information about you as to their own security. Also do not store credit card numbers with companies that you do business with online. It may be convenient for you to do so, but it exposes you to greater risk if there is a data breach. Finally, never click on any link in an email even one from a friend until you have confirmed that it is legitimate by contacting the friend directly to make sure that it was he or she that sent it. And even then you may wish to consider where they got the link to make sure that they are not unwittingly passing on malware to you.