Computer security, techniques developed to protect individual computers connected in a network from accidental or intentional damage . These damages include hardware malfunction , the physical loss of data and database access by unauthorized persons . Several simple techniques can hamper crime. For example , access to confidential information can avoid destroying the printed information , preventing others can see the computer screen, keeping the information and computers locked tables or removing sensitive documents . However, preventing cybercrime also requires more complex methods. In a system of so-called ' fault tolerant ' two or more computers simultaneously operate redundantly , so that if one part of the system fails the other takes over. Computer viruses are programs, usually destructive , which is entered into the computer ( to read a disc or access a computer network) and can cause loss of information ( programs and data) stored on the hard drive .