Hellhounds is an APT group targeting organizations in Russia, using a modified version of Pupy RAT called Decoy Dog. They gain initial access through vulnerable web services and trusted relationships, with a focus on the public sector and IT companies. The group has been active since at least 2019, maintaining covert presence inside compromised organizations by modifying open-source projects to evade detection. Hellhounds have successfully targeted at least 48 victims, including a telecom operator where they disrupted services.