Security Experts:

New CTB-Locker Variant Allows Victims to Recover 5 Files for Free

A new variant of the CTB-Locker (Critroni) ransomware has been spotted in the wild by researchers at Trend Micro.

The cybercriminals behind CTB-Locker have become more generous and more greedy at the same time. According to the security company, the latest version of the malware gives victims more time to pay the ransom and even allows them to decrypt some files for free. On the other hand, the ransom has increased significantly.

The threat has been distributed with the aid of spam emails, some of which are sent out by the notorious Cutwail botnet, Trend Micro said. The spam messages include an attachment containing a downloader component (TROJ_CRYPCTB.SMD).

Once the downloader is executed, the ransomware (TROJ_CRYPCTB.SME) is downloaded from one of several URLs.

The malware encrypts important files on the infected machine and displays a ransom demand. Victims are instructed to make the payment in Bitcoin via the Tor network.

Previous variants of the malware were designed to give users only 72 hours to pay the ransom money, but the deadline has been extended to 96 hours in the new version. Furthermore, victims are now allowed to decrypt five of their files for free.

Other crypto-ransomware, such as CoinVault, also include this free decryption feature, but they usually allow users to decrypt only one file. The cybercriminals are most likely trying to demonstrate that the files can be recovered, which is not surprising considering that many security experts advise users not to pay up because there is no guarantee that they will get their files back once the payment is made.

The new CTB-Locker demands the payment of 3 Bitcoin ($710), which is much more than the 0.2 Bitcoin charged by the older version.

The ransomware developers seem to be expanding the list of countries they’re targeting since the ransom message is now displayed in three new languages: Italian, German and Dutch. After the release of the new variant, Trend Micro noticed a spike in attacks, particularly in the EMEA region, Latin America, China and India.

CTB-Locker has been around since at least June 2014 and it was initially designed to target Russian speakers. The threat caught the attention of researchers because it was the first file encrypting ransomware to use Tor.

When it analyzed the malware in July, Kaspersky noted that CTB-Locker had been using an unusual cryptographic scheme.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.