Request Header Information

This information is contained in the header of every request you make to a web server.
Generally speaking, every time you browse to a page this information is sent to the server in plain text (unless the server uses https)
This information (and more) will be stored on each web server you visit in a form like this log sample (from our own server)

host	www.nagafix.co.uk
user-agent	CCBot/1.0 (+http://www.commoncrawl.org/bot.html)
accept	Accept: application/xhtml+xml,text/html;q=0.9,text/plain;
accept-language	en-us,en;q=0.5
accept-encoding	gzip
accept-charset	ISO-8859-1,utf-8;q=0.7,*;q=0.7
connection	close
cache-control	no-cache
pragma	no-cache

This information is used by the web server along with the networking information