Professional hackers, either working on their own or employed by government agencies or the military, can find computer systems with vulnerabilities lacking the appropriate security software. Once those vulnerabilities are found, they can infect systems with malicious code and then remotely control the system or computer by sending commands to view content or to disrupt other computers. There needs to be a pre-existing system flaw within the computer such as no antivirus protection or faulty system configuration for the viral code to work.