Perhaps you’ve heard of the latest computer malware.  It’s called Cryptolocker and it encrypts the files on your computer.  Not all of the files but the really important ones.  Documents, pictures,xls files essentially everything that you have on your system that is not needed for the system to boot up and run.  Except you will not be able to access for files because they are encrypted with formidable encryption.  You nor anyone else will be able to break it, or be able to brute force attack it.  At this point you are pretty much screwed unless that is you pay the ransom for the key.  The ransom costs $300 in bitcoins if you pay up in the first 96 hours, $2000. if your wait too long.  Nothing if you have made regular back ups of your data.
Back up your data now.  If you use a external hard drive for such purposes make sure to disconnect it physically from your system.  Only reconnect it to allow the back up process to complete, then disconnect it again.  USB drives are dirt cheap these days, get several of them and keep your files on these.  DVD’s are also dirt cheap and cannot be encrypted.  Keep your anti-virus programs up to date.  Nearly all reliable anti-malware programs allow for automatic updates, make sure that they are engaged and taking the required updates.  I personal use Avast on my wife’s Windows base machine.  AVG is also good and I can recommend that one as well.  It’s a favorite of the IT team when talking about free protection.  Use Secunia personal software inspector.  It will examine all of the software on you system and alert you to which programs require updating.  All of these are free for non-commercial use.  Microsoft Security essentials is also free and for me it worked with Avast installed and active.  I also recommend Super Antispyware to remove malacious spyware.  There is a free version of this available with reduced function.
Lastly, and I just did this today.  Comodo Desktop Security, makers of the best firewall in the business also makes a anti-malware suite that comes with their firewall.  It will take a suspicious file like cryptolocker and run it in the sandbox where it can do no harm.  Once it detects that the software is indeed malware, it give you the option to remove it.  The good people at Comodo state that their security suite is %100. effective.  Always back up your data, always.  Then you can tell the bad guys to go to hell.

I am not affiliated with any of the companies mentioned above.  I do use their products.