really, the only way I see to prevent this is to not look for www as an indicator of a URL. That would require that all URL's start with http:// or ftp://, etc..
by commenting out this line, all of the URL's above work fine:
'fString = ChkURLs(fString, "www.", 3)
but this one would not be recognized as a URL:
www.webhistory.org/www.lists/www-talk.1993q1/0262.html