The problem, though, is that the keys as stored on the user's system were encrypted. He and a researcher, Fabian Wosar of the Austrian security company Emsisoft, collaborated on a utility called the Emsisoft Decrypter that could recover the encrypted keys.
Vildoza knew he had made a big discovery, and one that would help a lot of people. In mid-March he had launched a blog chronicling his investigation, including an email address to request assistance.
At the time, he purposely withheld revealing the mistake CryptoDefense's authors had made on his blog. But Symantec then published a blog post on March 31 detailing the error.
Symantec's post described the file path where the keys were stored. But then around two days later, Symantec deleted that specific information.
Haley said the company had second thoughts about dribbling that bit of information since most users unfamiliar with RSA encryption wouldn't know what to do with it.
"I think while we thought it was technically accurate, we figured out it wasn't enough to really help anyone," Haley said. "The impression we left people was you could follow that, get the key and you're good to go."
He said people could have called Symantec's technical support for more information but acknowledged those people would have to be the company's customers.
After Symantec's post, Vildoza went ahead and described the problem on his blog. He received at least 80 emails asking for help, as well as unmanageable flood of spam, presumably as revenge from CryptoDefense's operators, who he suspects are Russian.
After the coding error in CryptoDefense became public, the malware authors fixed it, once again making the malware an intractable problem for those infected.
Haley said he understood the argument for keeping the mistake quiet. But the cybercriminals would have figured "it out eventually and closed that loop," he said.
The utility developed by Vildoza and Wosar only works for versions of CryptoDefense that infected machines prior to March 31. But it still has helped many people.
Dan Getty, who is responsible for desktop patch management at the University of Michigan in Flint, said CryptoDefense infected two computers, including one of an administrator that contained thousands of files which were not backed up.
"The loss would have been catastrophic," he said via email.
Michael Van Rheenen, director of development for the online software company Tallyfox in Zurich, wrote via email that he briefly considered paying the ransom after three computers and a storage drive were infected.
But the "absurd abuse" aspect of the attack "led me to keep searching for a possible solution for it," Van Rheenen wrote. He eventually recovered 5,675 files, ranging from documents to photos, none of which had been backed up.
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