Hackers are capable of a lot, they will always have a reason for hacking, whether its for your details or just for the hell of it. Hackers will probably hack because: 

They want to vandalise: Destruction or digital defacement of a computer or its data for destruction’s sake. Sometimes this is ego-driven. They break in and leave their mark to show they’ve been there.

They are a hactivist [4]: A form of vandalism or electronic civil disobedience with a political agenda. Usually hacktivists have altruistic motives.

They want to steal something, maybe to resell

They want to hijack something: Many of the financially motivated hackers are interested in using viruses and Trojan horses to hijack your computer so they can remotely control it for their own purposes.

They want to steal your identity (identity theft): Electronic theft of personal information that can be used to steal financial resources from an individual or corporation.

It is hard to do but hackers can be stopped from getting into your computer and accessing all your files, you just have to be careful on the internet. Here are some pointers on how to stop hackers:

1. BEWARE OF SPIES AND KEYLOGGERS [4]: There are programs that can spy into your computer. It happens when people download a program (such as a game) that comes bundled with "Sputnik" or "VX2" or another brand of spyware. It installs itself silently on your computer and then monitors your "clickstream" as you navigate around the web, sending information about your activities (including credit card numbers!), back to the originator.

2. DELETE UNKNOWN EMAILS: If you receive emails from random people’s names, do not bother to open the email, just delete it. If you have any doubts after reading the name and the subject, it’s probably not someone you know. Never download or open attachments unless you are sure it’s from someone you know. Give the person a call quickly and ask them if you’re not sure. Most large companies that you create online accounts with will not send you attachments unless you specifically ask for them through their website. Also, be wary of any emails from sites pretending to be banks, auction sites, etc asking for you to verify bank account info or address info. No bank ever does that. Neither will any email address companies eg. Windows Live Hotmail, Yahoo! Mail...

3. SECURE YOUR WIRELESS NETWORK: Most wireless routers are set to no security when you install them. Be sure to log into the router and at least set the basic security that requires a password. There are stronger encryption [4] options, but if you don’t understand those, then simply set a password on the router, otherwise anyone can connect to your home network and access everything.

4. USE A COMPLEX PASSWORD: This means that you should already have a password to login to your computer. Not having a password at all is not a good idea. Create a password for all user accounts and make sure it’s complex. Complex means it should have numbers, upper case characters, lower case characters, and symbols. This makes it way more difficult for a hacker to get into your computer.