I do believe these sites do work as long as your IT dept doesn't know what the site is, then they'll block it too. So I guess you'll be browsing teh **** from work now, eh?
Of course, if your IT dept finds out about it they could go checking user's history and see if they've been visiting it. Also, firewalls typically log the sites that have been visited, but it varies as to how long they keep the log and whether the IT folks check it regularly. Assuming they have the time or would bother with the effort. In my experience IT departments are usually under-staffed anyways, and have plenty to keep them busy. I know that we would just block the site and leave it at that, unless it was found that a user was utilizing the site for some malicious effort.
Thanks for the link btw, I'll be adding it to our blocked list.
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