possibly damaging remote operation to occur.  The unsafe URL is
   typically constructed by specifying a port number other than that
   reserved for the network protocol in question.  The client
   unwittingly contacts a server which is in fact running a different
   protocol.  The content of the URL contains instructions which when
   interpreted according to this other protocol cause an unexpected
   operation. An example has been the use of gopher URLs to cause a rude
   message to be sent via a SMTP server.  Caution should be used when
   using any URL which specifies a port number other than the default
   for the protocol, especially when it is a number within the reserved
   space.

   Care should be taken when URLs contain embedded encoded delimiters
   for a given protocol (for example, CR and LF characters for telnet
   protocols) that these are not unencoded before transmission.  This
   would violate the protocol but could be used to simulate an extra
   operation or parameter, again causing an unexpected and possible
   harmful remote operation to be performed.




 
RFC 1738            Uniform Resource Locators (URL)        December 1994


   The use of URLs containing passwords that should be secret is clearly
   unwise.

7. Acknowledgements

   This paper builds on the basic WWW design (RFC 1630) and much
   discussion of these issues by many people on the network. The
   discussion was particularly stimulated by articles by Clifford Lynch,
   Brewster Kahle [10] and Wengyik Yeong [18]. Contributions from John
   Curran, Clifford Neuman, Ed Vielmetti and later the IETF URL BOF and
   URI working group were incorporated.

   Most recently, careful readings and comments by Dan Connolly, Ned
   Freed, Roy Fielding, Guido van Rossum, Michael Dolan, Bert Bos, John
   Kunze, Olle Jarnefors, Peter Svanberg and many others have helped
   refine this RFC.




































 
RFC 1738            Uniform Resource Locators (URL)        December 1994


APPENDIX: Recommendations for URLs in Context

   URIs, including URLs, are intended to be transmitted through
   protocols which provide a context for their interpretation.

   In some cases, it will be necessary to distinguish URLs from other
   possible data structures in a syntactic structure. In this case, is
   recommended that URLs be preceeded with a prefix consisting of the
   characters "URL:". For example, this prefix may be used to
   distinguish URLs from other kinds of URIs.

   In addition, there are many occasions when URLs are included in other
   kinds of text; examples include electronic mail, USENET news
   messages, or printed on paper. In such cases, it is convenient to
   have a separate syntactic wrapper that delimits the URL and separates
   it from the rest of the text, and in particular from punctuation
   marks that might be mistaken for part of the URL. For this purpose,
   is recommended that angle brackets ("<" and ">"), along with the