From the time the National Science Foundation (NSF) assumed responsibility for the U. S. Internet backbone, they anticipated a transition to commercial use. There were a few commercial ventures in the 1980s, like the Clarinet News Service, CARL UnCover for scholarly documents, and the Computists’ Communique electronic newsletter, but the NSF acceptable use policy and Internet culture were largely non-commercial. NSF is phasing out their support, and commercialization is taking off — you can even order pizza.
– Commercialization of the Internet, Communications of the ACM, November, 1994.
The spread of commercial messages on the Usenet has made some newsgroups almost unusable.
Up until 1994, the Usenet was used only for non-commercial purposes under the protection of NSFNET policy. That all changed that year when two lawyers, Canter and Siegel, sent an advertisement for an immigration service costing $99 to more than 6000 newsgroups at once, sharply increasing the noise to information ratio on the the Usenet by several times. The Usenet population was enraged.
Many people posted messages describing how to obtain the same service for free. Many more sent the two lawyers thousands of junk email to ensure that any legitimate responses would be buried in protest messages, and loaded up their Internet service provider with more than 200 megabytes of messages in less than two days. The story had global impact, and was covered by all of the major news organizations.
Today, some newsgroups are so saturated with advertisements they are almost unusable. At the same time, the Usenet is a living space, and many groups are still mostly ad free while others are created when necessary to start a new group afresh. Establishment of an information only network has been the primary impetus behind development of the Usenet II system.
Resources. Wikipedia page on Cantor and Siegel is here.