Locky ransomware activity ticks up

Computer security companies say it has become a commonly seen type of ransomware, which is used to hold a computer’s files hostage pending a ransom payment.

Trustwave's SpiderLabs said on Wednesday that 18 percent of 4 million spam messages it collected in the last week were ransomware-related, including many linked to Locky.

"We are currently seeing extraordinary huge volumes of JavaScript attachments being spammed out, which, if clicked on by users, lead to the download of a ransomware," wrote Rodel Mendrez, a Trustwave security researcher.

Locky is distributed through spam messages that have been sent through the same botnet used to send Dridex, the infamous online banking malware.

At first, the spam messages contained malicious Microsoft Word documents with macros that would download Locky. But McAfee wrote on Monday that recent Locky spam contains an obfuscated JavaScript file, which if executed downloads the ransomware.

"We believe the change to JavaScript is to evade antimalware products due to its obfuscation and small size, which suggests the file is benign," McAfee wrote.

Security vendor Fortinet studied statistics collected by its Intrusion Prevention System software between Feb. 17 and March 2. The software detects when ransomware connects to command-and-control servers used by cybercriminals to manage the malware.

It found that about 16.4 percent of 18 million communications it detected were for Locky infections, with the rest belonging to CryptoWall and TeslaCrypt, the other top ransomware families.

"As predicted, Locky already covers a big chunk of the infections," wrote Roland Dela Paz, senior antivirus analyst with Fortinet.

Most of the Locky infections appear to be in the U.S., France and Japan, he wrote.

The FBI has warned that ransomware has become one of the biggest threats to consumers and businesses. Although some ransomware writers made mistakes in their code early on, there's usually no way to recover the files if the decryption key is not released.

The ransom is usually a few hundred dollars, with detailed instructions displayed to victims for how to pay in bitcoin. Security experts generally recommend backing up files to recover from a ransomware attack and ensuring the backup drive can't be reached by malware.