This article is from the SSH - Secure Shell FAQ, by Thomas Koenig Thomas.Koenig@ciw.uni-karlsruhe.de with numerous contributions by others.
As with every piece of freely available software, this is difficult to
find out. The best current estimates are that at least 1000
insitutions in 40 countries use it. This estimate is based on
o The number of people on the ssh mailing list, around 600, from 40
different countries and several hundred domains
o Each week, the ssh home pages are accessed from roughly 5000
different machines, many of them web caches; also, these machines
often are different from week to week.
 
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