You need to restore the files from backup to be able to gain access to them again or if you don’t have a backup, then hopefully you have a trace of the virus left so you can pay the $300 ransom to unencrypted the files. The ransomware that is doing the rounds is Cryptolocker and this scans local and network files and will encrypt a variety of files that it is configured to find.
There is a good write-up about it here:
http://blog.malwarebytes.org/intelligence/2013/10/cryptolocker-ransomware-what-you-need-to-know/
Perhaps this authoritative source will also help you.
https://forums.adobe.com/message/6978758#6978758
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