These creations are referred to as worms or viruses. A computer virus typically enters your computer trough an infected floppy disk. After this disk is inserted it copies itself into your computer and to all floppy disks you subsequently use in your system. A virus can hide on the boot sector of a floppy, attaches itself to an existing program, often in the computer's operating system, or may disguise itself as a legitimate program. Viruses not only can spread from one computer to another by way of exchanged disks but also through programs sent via telephone lines.
Worms are self-contained programs that enter a computer and generate their own commands.
Logic bombs, viruses, and worms, if undetected, may be powerful enough to cause a whole computer system to crash. Computer professionals are often amazed by the ingenuity of the hackers at finding ways to sabotage the legitimate work of other computer professionals. Clinicians using computers in medical applications must be aware of the possible vulnerability to these malicious attacks that could jeopardize the confidentiality and safety of the patient.