That's just the question isn't it...
Qu13e is a long running ARG, which has been around since 2001. Through the years the site qu13e.com has changed, recently reappearing after a long time of silence.
There has been an incredible amount of work/research conducted on the ARG over the years, much of which has taken place at forums.unfiction.com
If you would like more on the subject, you can visit a translated english version of the original German wiki (Errors are to be expected through translation) at http://www.microsofttranslator.com/bv.aspx?from=de&to=en&a=http%3A%2F%2Fwww.argwiki.de%2Findex.php5%3Ftitle%3DQU13E_-_Trail