CryptoLocker encrypts files on your computer and then demands that you pay for the key to unlock them. Your anti-virus software likely won’t protect against it – but there are some effect tools, including Microsoft’s Enhanced Mitigation Experience Toolkit (EMET) and third party utitlies such as
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http://windowsitpro.com/security/2-utilities-protect-your-network-and-pcs-cryptolocker-malware