The aggressive efforts put into code obfuscation make Blackhole one of the most persistent threat campaigns experienced to date. Each day we encounter thousands of new, unique files for the various components used in the kit. The structure of the Blackhole landing page is regularly updated, in some cases reverting back to tactics used several months previously. The most recent of these include the use of Math functions, presumably as an anti-emulation technique. The main techniques for obfuscating JavaScript have already been described in detail.”]
Source: https://nakedsecurity.sophos.com/exploring-the-blackhole-exploit-kit-10/