Hacker is a term from old Internet (pre-Crash of 2029) for a Person, that uses computers and networks in an illicit way. In the era of wired Matrix the term "Hacker" was replaced by the term "Decker" - a word, created by combining "Hacker" and "Cyberdeck". After the second Crash (the Crash of 2064) and the Wireless Matrix Initiative the term "Decker" was replaced again by the older term "Hacker" because he doesn't need a cyberdeck anymore to manipulate the new, wireless matrix, because he can do it just with a commlink. And to confuse matters more, in 2075 GOD rolled out a new wireless protocol for the Matrix. To bypass the new protocols you now need a device called a "Cyberdeck". Which has brought back the term "Decker" and the term "Hacker" has become a generic term to describe anyone that is capable of subverting Matrix security, which includes Technomancers and Riggers.
See also: Decker.