Virus
Most people forget to close ports using firewall software and not monitor Denial of service attacks they can bring computer to a halt in matter of minutes. I was running a system using IIS sever and had an instructor in college told him that my system was secure he could not hack in he set a denial of sevice attack at every port while I was trying to close the ports I forgot it sap the computer resources and let in a torgan and he had full control of my computer the lesson I learn is if you are getting attack disconect it from the network is the only reliable option and regroup better run to fight again than to be taken over and no control