A ransomware Trojan threat is back – in an even more noxious form – two years after it last appeared.
A new variant of the GpCode ransomware encrypts user files on infected Windows PCs using theAES 256 and RSA 1024 encryption algorithms. The malware only encrypts the start of media or Office files, but that's enough to make any data recovery process difficult if not impossible.
The latest version of the malware overwrites data in files instead of simply deleting files after encryption, the approach taken by previous versions of GpCode. The approach makes it far harder to use data-recovery software.
The unknown miscreants behind the Trojan – who first started operating in 2004 but have been quiet since 2008 – then demand $120 for keys needed to decrypt files, via a notice displayed on infected machines after the malware has scrambled user files. Other ransomware scams have cropped up over the last two years, but none of these involved variants of the GpCode Trojan, according to net security firm Kaspersky Lab.
A write-up of the attack, together with screenshots, can be found in a blog post by anti-virus analyst Vitaly Kamluk of Kaspersky Lab here. Victims are instructed to send funds via a wire transfer if they ever want to see their data again.
Sophos adds that the malware apparently comes via a drive-by vulnerability from compromised websites, A malicious PDF is reportedly used to download and install the ransomware, which only affects Windows PCs.
Users are advised to regularly back up sensitive data and to use security software as a precaution against possible attacks. ®