Unknown programs requesting access
Computer security programs and firewalls help restrict access for security purposes. If the computer prompts for access to program you do not know, rogue programs may be installed, or it may have been hacked. If you do not know why a program needs access to the Internet, we recommend blocking access to that program. If you later discover these blocks cause problems, they can be removed.
Tip: A firewall prompting you for access may also just be someone trying to probe your Network looking for open or available ports.
Security programs uninstalled
If the computers antivirus, anti-malware program, or firewall that has been uninstalled or disabled, it can also be an indication of a hacked computer. A hacker may disable these programs to help hide any warnings that would appear while they are on your machine
Computer doing things by itself
When someone is remotely connected to a computer they can remotely control any device. For example, a mouse cursor could be moved or something could be typed. If you see the computer doing something as if someone else was in control, this can be an indication of a hacked computer or If the computer is dialing the Internet on its own, it is an indication that a program needs to connect to the Internet. It is common for programs like e-mail clients to do this to check for new e-mail. However, if you cannot identify what program needs Internet access, this can also be an indication of a hacked computer.
Internet browser home page changed
New toolbar Internet browser changes such as your home page changing to a different web page, a new toolbar getting added, your search provider changing, web pages getting redirected are all signs of a browser getting hijacked and not a computer hacker.