Computers can be really strange and fickle when they want to be. For a machine that is based on logic there seems to be a lot illogical decisions that go into the creation of them. Well that is at least true when it comes to the software that runs these machines. When it comes to each operating system there seems to be an ideology that you have to figure out along with the general instructions on how to use the thing. When it comes to the instructions of a computer you can just read the book that came with it and you should be fine. When it comes to the ideology of the operating system that you are using, that can be a whole lot trickier and something that may take you awhile to get used to.
That is why people have such a hard time when they switch from a PC to a Mac or from a Mac to a PC. The ideologies of the machines are very different and you have to get used to how each one of them works. For some people it only takes a few days and for other people it may take a few months of them constantly using the device.
While each operating system does have a unique way of doing things, you will see from time to time that they take ideas off of each other. We have seen that recently with Windows and the way that it handles security recently. When you are on a UNIX based machine like Mac OS X and Linux you have to deal with something called different users. And before the computer is able to do anything, the user has to give permission for that action to happen. Say for example if you wanted to install a program on the computer, you would need to give the program permission to be installed. You would do this by typing in su or sudo and then typing in your password. Windows until recently did not work that way. Yes, Windows did have the different user paradigm but by default everyone ran as administrator, which meant that they could do anything that they wanted. You would have to downgrade the other users to guest if you did not want them to have that level of control over the machine.
But now that is no longer the case. The Windows developers have taken their cue from the other operating systems out there and no you no longer can just install any program that you want to. Not only do you have to be an administrator but you have to give specific permission for the program to run. Without that permission there will be no install.
But you still have to be careful on a Windows machine. Other people on the machine can still run as an administrator while they are using the machine. And while they are the administrator they can give permission to an app that may be able to harm your computer. The whole point of asking permission is so an app cannot be installed behind your back. If you have someone with administration privileges that says yes then there is nothing that the operating system can do.
That is why you need to make sure that when it comes to your machine, you are the only one who is running as administrator and you are the only one who is able to make changes.