Originally, a
scam run by the Dutch telco
PTT Telecom: a private intranet with limited Internet access, advertised as the real thing.
They actually trademarked the term ("het Net", which just means "the Net") and used it as its name.
Internet users already used that term to refer to the Internet, of course; this private netwerk got to be known as
Het Net Niet.
The network gradually become more open and, like its American predecessors such as [AOL} and Compuserve, basically turned into a regular ISP; domain hetnet.nl.