Logic Bombs and Time Bombs

Like other viruses, logic bombs are designed to cause harm to your computer. Logic bombs, however, only trigger when specific conditions are met. For example a computer programmer may insert code into a payroll program that deletes files if her name is not found on the list. This means that files will be deleted if she is ever fired. A company named Omega Engineering lost millions of dollars as a result of a logic bomb left by a former employee.
Other viruses, called time bombs, may only detonate on a specific date or time. An example of this is the Jerusalem virus which, every Friday the 13th, deletes all the files on an infected computer.