Just another suggestion. Do you have a firewall? If not, please consider installing one of the following:
ZoneAlarm is more automatic so a bit little easier to use; Comodo gives you a better overview so you can see more easily what is being blocked.
If your computer is being hacked, following lowtek's advice as well as making sure your security settings are at least set to medium and installing a firewall should help.
Please note that there are other reasons for erratic behavior from a mouse. Is the mouse wireless? What company makes it? Are there other computers in your home that are also using a wireless mouse? I do know of a case where a child in one room was using a mouse and causing movement in his father's mouse because their signals got connected. This also caused programs to turn on and off. If it is a wireless mouse, you may want to check it by substituting in a wired mouse.