The bad guys are gaining access to web-based email accounts (Yahoo-mail, Gmail, Hotmail) and hiding the contents, like your contacts and messages. When you log on, all you find is a message from the Hijacker demanding that you pay if you want to have your information restored.
This attack can occur when the bad guys capture your user ID and password from a computer that is infected with a keystroke logger. A keystroke logger is software OR hardware that records all of the keystrokes made on the computer.
Cyber cafes, libraries, and other locations with "public" computers are often targeted by the bad guys, because they know that a wide variety of unsuspecting people will type in their most important information ( i.e. user ids and passwords).
There is no way for the average person to thoroughly check a public computer for the presence of software-based keystroke loggers. If you don't know what you are looking for, even hardware keystroke loggers can be difficult to find. The moral of this story: be very cautious if you choose to use public computers. The risks are greater than you think.
News Article on Cyber Hijacking