Security researchers at Trustwave SpiderLabs have published a technical review about important changes made in version 2 of the Blackhole Exploit Kit. Apparently, the main focus of version 2 is about evasion techniques, that is, avoiding detection by anti-virus solutions and other security tools rather than on new obfuscation techniques.
Read the full review here – http://blog.spiderlabs.com/2012/09/blackhole-exploit-kit-v2.html