Researcher: Malware, Increasingly Interdependent, Stifles Security Wares | threatpost:
"Rather than operating independently, the BlackHole BEP relied heavily on the Zeus malware family to spread - and vice-versa, Sood found. The Zeus malware relies on BlackHole's anti-malware tracking features, whereas Sood observed BlackHole uses the Zeus database of infected hosts to spread, harvesting specific details about the Zeus-infected target and then launching attacks that would trigger infections on that host, Sood said."