> Is there any elaboration on what "effectively controls access" means
Apple Inc. v. Psystar Corp.[1] involved circumvention of a system that "effectively controls access" to Mac OS X, preventing it from being installed on non-Apple hardware.
Apple's anti-circumvention system is (in part) that some of the important system binaries are encrypted, the kernel transparently decrypts them when they are executed.
The key isn't secret (in fact it's a constant that hasn't changed in 10+ years), but it is only distributed inside the SMC chip on the main board of a real Mac.
There's no question that encryption is generally an effective access control method, it can't be circumvented without either having the key or breaking the encryption system in use.
The court found that regardless of how trivial it was to obtain the key, the fact that it was encrypted made it "effective":
> Psystar contends that Apple's anti-circumvention technology was ineffective because the decryption key for circumvention is publicly available on the internet. This argument fails.
> "The fact that circumvention devices may be widely available does not mean that a technological measure is not, as the DMCA provides, effectively protecting the rights of copyright owners in the ordinary course of its operation." Sony Computer Entm't Am., Inc. v. Divineo, Inc., 457 F. Supp. 2d 957, 942 965 (N.D.Cal.2006).
> Generally, measures based on encryption "effectively control" access to copyrighted works. Here, when the decryption key was not employed, the encryption effectively worked to prevent access to Mac OS X. And that is all that is required.
> See Universal City Studios v. Reimerdes, 111 F. Supp. 2d 294, 318 (S.D.N.Y.2000) (noting that when a decryption program was not employed, the encryption worked to control access to the protected work).
> Accordingly, Psystar has violated the DMCA by circumventing Apple's protection barrier and trafficking devices designed for circumvention. Apple's motion for summary judgment on its DMCA claim must be granted.[4]
[1] https://www.courtlistener.com/opinion/1557201/apple-inc-v-ps...