Security experts say coding mistakes in a malicious program that encrypts data mean anyone affected by the power worm virus will not be able to recover files.
A variant of Power Worm destroys keys that could help recover any data that it scrambled. The news comes as hackers produce a new type of ransomware aimed at websites and encrypts data sitting on servers.
Power Worm can infect Microsoft Word and Excel files, however the latest update has been adapted to go after many more of the data files it finds on a victim's machine than it usually would.
Nathan Scott, malware researcher, discovered the variant and uncovered the mistakes its creator made when updating it.
Mr Scott believes the problem with the malware arose when the creator tried to simplify the decryption process.
The aim appeared to be that just one encryption key would be needed but in doing so they mangled the process of generating it. Because of this there is no key created for the files it encrypts when it compromises a computer.
Malware researcher, Lawrence Abrams, said: "There is unfortunately nothing that can be done for victims of this infection.
"If you have been affected by this ransomware, your only option is to restore from a back-up."
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