Newark, it's been illegal in the UK since at least 1990 (the Computer Misuse Act), punishable by jail and/or a fine.
However, most users do agree in one way or another to this stuff being installed (viz. the 180 Solutions EULA above), although the agreement is highly questionable ethically; it is usually buried in the depths of click-through agreement for some other piece of software, so very few users will even be aware the agreement exists.
For example, i've just read the Kazaa EULA (saddo, huh?
) - it's actually unusually short and unobfuscated, but still contains the usual: s9.1 requires you to install "third party software", including (without limitation) a list they helpfully provide in s9.4 (cydoor, TopSearch, GAIN AdServer, Instafinder). Under s.3.5 you may not block or remove any of this software. So ... by installing Kazza, you've agreed to install this cr@p. It's not Misuse, it isn't even illegal, because you said "yes" to it.