My brother built me a computer for my birthday from hardware modules that he bought. I've been using it for about 5 months. My PC has total open access, as it was an offer, and I didn't want to lock it with a password as it would seem ungrateful.

Usually, for privacy, all that I do is to clean it regularly with CCleaner and also clean internet history, cookies and internet temporary files on Internet Explorer Options. I am always careful signing out of e-mail, YouTube and other internet sites, and I never oblige when the system asks me if I want to be remembered when I login for a new session.

However, one of these days, I arrived earlier than expected from college and found out my brother with my Gmail session opened and also my Youtube session viewing the late of my favorite videos!! I'm totally sure that, before going out, I didn't forget any of the security procedures described above. I dismissed the case as I didn't want to quarrel in front of our parents but I'm not going to accept this and I'm asking you for help.

As you already guessed my brother knows a lot about computers. Also he recently finished with his girlfriend because he found internet information in her computer that made him think that she was unfaithful. He is very suspicious and after that event I saw this coming...

How does he manage to do this? Does he go to a folder in my system and looks for cookies or something like that? So what I want to ask you is:

- What can I do to protect my privacy besides opening Windows XP with a password or returning to my old laptop?
- How can I trustfully clean or avoid access to my cookies, internet history and private files.
- What surveillance software can I acquire to monitor PC activity while I'm gone (I don't mind if the software is visible because I also want it to serve as a warning: "keep away from this limit!".
- What software can I acquire that successfully hides folders from indiscreet viewing.
- What extra measures should I keep in mind.

I'm very grateful for your attention. Please don't mind my English because I'm Portuguese. Thanks!