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DENVER — A new type of malware called the CryptoLocker is gaining popularity on the Internet because it holds files on your computer ransom.

The malware is spread through phony emails that are designed to look like they are from legitimate business. Some appear as fake UPS or FedEx tracking notifications.

Once opened, CryptoLocker installs itself in the “Documents and Settings” folder, scans the hard drive and encrypts certain file types, including documents associated with Microsoft Word, reported the International Business Times.

The program then launches a pop-up window with a 100-hour countdown and a demand the computer owner pay a ransom to get access to their files again.

If the user does not pay up, the key to decode the files is deleted. Advanced software security companies say there is no way for them to retrieve the files once they have been encrypted.

The hackers that spread the virus cover their tracks by demanding payment in Bitcoins, a digital currency designed to be as anonymous as cash.

CryptoLocker is the most dangerous type of malware, commonly called ransomware, to show up in recent months.

The good news for users is that paying the ransom does actually decrypt the files.

The best way to protect yourself is to follow basic e-mail safety procedures. Do not open an attachment unless you know where it is from and you are expecting it.