Network Wizards notes that there are 6.64 million host computers on the Internet. Of these, 2.37 million are international hosts representing 150 countries. Unfortunately most of these are for members only. They uniquely have a robot called ZONE which counts the number of hosts on the Internet. Lots of useful information here.
Surveys abound, using all sorts of measurement parameters.
However, from observing many of the published surveys over the last two years, here is an educated guess as to how many are online worldwide as of December 1998. And the number is 151 million. It cautions that while usage has soared, there are fundamental problems to be overcome before Britain can boast a competitive and profitable e-commerce economy. The basic figures are good. 20 percent of the UK population have used the Internet in the past twelve months.