Hi,
It is a type of program that literally hijacks the computer, leaving it virtually static. After the attack, the program informs the owner of the computer that will only release the machine to use for payment. Examples of ransomware: Gpcode AK, and Krotten Archiveus.
The care you must have: How the other threats, the ransomware not come into your machine without your help - albeit indirectly. Care to share files and network with links and emails that ask you to install suspicious programs that can "improve their safety." Keep your antivirus and antispyware programs updated and trust his judgment when opening a site: it usually tells you when a page is suspected.
hugs