Hacking can mean a number of things, but computer hacking is basically when someone accesses your computer or its resources without your permission and initially without your knowledge. Computers can be hacked without leaving evidence behind. As a home user, you can almost always find out if you have been hacked because the hacker either wants to keep using your computer resources or wants to harm your computer.
Look for extra folders, which may take time. Right-click on the hard drive in Windows Explorer. You will see how much of your hard drive is being used. If you notice you suddenly have a lot less hard drive space, that is a warning sign that your computer may be being used to share files online, such as illegal movies. Go through the folders on your computer one at a time to look for folders that are large in size that you did not put there and that are not valid system files.
Check the users. Go to the Control Panel and click on "Users." If any extra users have been added or if some user passwords have been changed, this is a sure sign that the computer was hacked.
Find out if your security has been shut off. Go to the Control Panel and look to see if Windows Firewall is turned off. Sometimes it will be impossible to turn back on. Make sure your antivirus is on and that Windows updates are turned on. These things are often disabled when a computer has been hacked.
Run your antivirus and spyware remover programs, doing a full scan with each software. Often hacked computers have viruses and a lot of spyware programs.