"Circumvention" is the new crime created by the
Digital Millennium Copyright Act, section 1201, a.k.a. the anticircumvention provision.
1201 makes it illegal to "circumvent a technological measure that effectively controls access to a work protected under \
copyright\", or create or distribute tools to circumvent access or copy controls. This means that if a publisher encrypts something before distributing it, it's now illegal to decrypt, even if the encryption robs you of fair use rights in the material. (And "effective" doesn't mean decent, either, only 'having the effect of'.)
The anticircumvention provisions are currently being challenged in Universal v. Reimerdes (the DeCSS case), Felten v. RIAA, and U.S. v. Sklyarov. A number of computer scientists, cryptographers, and law professors have joined the outcry calling this statute unconstitutional.