If you're interested in computer security and you want to study the subject in detail, you could do worse than to get yourself a copy of the Computer Security Handbook. It's a thorough study of the subject, from a respected academic publisher, and runs to more than 2,200 pages. It does, though, cost $130.
But if you're quick, you can get it for free. And thankfully it's delivered as a 28 MB PDF file, rather than on paper!
Simply head to http://betanews.tradepub.com/free/w_wile234/ and enter your email address, and you'll get the download link by return. The offer expires on May 10th 2017.