how do I sign out of my computer?

99.9% of the people who claim to be hackers couldn't hack their way out of a wet paper bag. I wouldn't worry to much about it.

While it is true that anyone on any operating system, including Macintosh and even phone systems, it is highly unlikely. It would take a large amount of effort and would yield little 'valuable' information. (Mot hackers who would spend that time are probably hacking Sony right now anyways). When in doubt, install a security tool such as free AVG and turn off the computer at night (this also saves power). Nobody can access a computer that has been turned off as far as I know)

Very true. Good hackers can hack into anything. Just look at the PlayStation 3 network, some random dude hacked into their system and screwed them up for months. You could try to get some sort of secredity software on your computer.

i doudt it very much that someone could hack into ur system and delete stuff without you knowing when really you might have a secrity program and a viruse program on your system so in the end it would be false be if you dont have SECURITY PROGRAMS AND A VIRUSE PROGRAM ON YOUR SYSTEM then someone could hack it so have your computer protected against hackers

That's a rare occurrence.

I wouldn't care about it much, but if you feel scared of it, disconnect the internet when you don't use it.

Yes thats true. i recommend you disconnect from the internet whenever your not using you computer