On February 14th, 2003,
Opera Software released a special version of their
web browser which would behave differently from the standard Opera 7.01 in exactly one way. When you browse to www.msn.com with it, that page is automatically translated into the
Bork language of
the Swedish Chef.
The reason? It had become apparent that Microsoft was deliberately sending a different, distorted version of the MSN website to any web client which had the string "Opera" in its User-Agent header. Opera Software apparently wanted to make a point that if webservers and browsers don't stick to open standards, things can quickly get downright silly.
For the full press release, see:
http://www.opera.com/pressreleases/en/2003/02/14/
For technical details from the Opera CTO:
http://people.opera.com/howcome/2003/2/msn/