Ransomware is getting more complex, and anti-virus companies are worried they may not be able to decrypt ransomed files, according to a new report.

Malware Evolution: April to June 2006, Hidden Wars by anti-virus company Kaspersky Labs warns that ransomware authors are creating more sophisticated encryption algorithms in a bid to outfox security companies, blackmail users and companies.

"We were able to decrypt 330- and 660-bit keys within a reasonably short space of time, but a new variant, with a longer key, could appear at any time," said Aleks Gostev, a senior virus analyst at Kaspersky Lab. "If RSA, or any other similar algorithm that uses a public key, were to be used in a new virus, anti-virus companies might find themselves powerless, even if maximum computing power was applied to decrypting the key."