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What is this
Everything you need to complete the mission is right there.
If you don't know what something is, listen to everyone on this site and google it. In this case, go to google and type 'http user_agent' then click the 'SEARCH' button.
Also check out http header information and if you're starting to understand what's going on, go to http://www.proxomitron.info/
MAJOR NOTE: using this program is just one of countless ways to do it… to get the most out of each challenge, attempt them several times using multiple methods.