The above domain is the location for the
Los Alamos National Laboratory repository of
e-Prints for technical papers. It is run by the
United States Department of Energy. It is an entirely professional site, and the domain has existed since at least 1991 (The domain predates around 100% of the web!). It houses top notch
physics and
mathematics research. For the record, the web page has nothing whatsover to do with
pornography.
However ... the
triple-x in the
URL causes it to be routinely filtered out by aggressive
censorware products. When this occurs, the domain can also be accessed by the mirror URL at arXiv.org