This question is a broad questions and can be answered in many different ways.
Yes.
With today's technology you can even buy software programs that allow you to gain access to your own computer remotely. Let's say you have files on your home computer and you need something from it while your at work, this is one way it could happen.
If you allow a virus or other harmful software to run on your computer it may do things others want it to do with out your permission.
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You need a crossover cable for that.
A computer network adapter is used to connect a computer to the internet source that is provided by a modem. The only exception is the wifi router when it comes to the discussion on what is better.
Fiber Optic networking allows computers to communicate with a beam over light oven thin strands of glass cabling.
A computer attack is basically either when a hacker is on your computer doing things that you can do. Or it can be a Virus
It just means to hold your mouse over something.