New pro-Ukraine hacker group targets Russian companies with custom ransomware

F6 links new pro-Ukraine ransomware group VantaCore, likely a Thor rebrand, to seven attacks on Russian firms using custom tooling and multimillion-dollar demands.

Russian cybersecurity firm F6 reports that VantaCore, a ransomware group believed to be a rebrand of pro-Ukrainian group Thor, has targeted at least seven Russian organizations with ransom demands reaching millions of dollars, operating as a ransomware-as-a-service operation with a Tor-based victim chat and a leak site. The group uses custom-built tooling including the VantaCore ransomware that encrypts servers and workstations, VantaCoreLoader for distribution, the VantaCoreRAT backdoor, and SnowKiller, which disables antivirus and security software. Initial access relies on poorly secured VPNs and remote-access tools, flaws in internet-facing applications, and credentials stolen from business partners. F6 notes pro-Ukrainian groups increasingly abandoned stock ransomware like LockBit 3 Black and Babuk in 2025-2026 in favor of custom malware.