Software bug

A software bug is an error, flaw, failure or fault in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. The process of finding and fixing bugs is termed 'debugging' and often uses formal techniques or tools to pinpoint bugs, and since the 1950s, some computer systems have been designed to also deter, detect or auto-correct various computer bugs during operations. Most bugs arise from mistakes and errors made in either a program's source code or its design, or in components and operating systems used by such programs. A few are caused by compilers producing incorrect code. A program that contains a large number of bugs, and/or bugs that seriously interfere with its functionality, is said to be buggy (defective). Bugs can trigger errors that may have ripple effects. Bugs may have subtle effects or cause the program to crash or freeze the computer. Other bugs qualify as security bugs and might, for example, enable a malicious user to bypass access controls in order to obtain unauthorized privileges. Some software bugs have been linked to disasters. Bugs in code that controlled the Therac-25 radiation therapy machine were directly responsible for patient deaths in the 1980s. In 1996, the European Space Agency's US$1 billion prototype Ariane 5 rocket had to be destroyed less than a minute after launch due to a bug in the on-board guidance computer program. In June 1994, a Royal Air Force Chinook helicopter crashed into the Mull of Kintyre, killing 29. This was initially dismissed as pilot error, but an investigation by Computer Weekly convinced a House of Lords inquiry that it may have been caused by a software bug in the aircraft's engine-control computer. In 2002, a study commissioned by the US Department of Commerce's National Institute of Standards and Technology concluded that 'software bugs, or errors, are so prevalent and so detrimental that they cost the US economy an estimated $59 billion annually, or about 0.6 percent of the gross domestic product'. The Middle English word bugge is the basis for the terms 'bugbear' and 'bugaboo' as terms used for a monster. The term 'bug' to describe defects has been a part of engineering jargon since the 1870s and predates electronic computers and computer software; it may have originally been used in hardware engineering to describe mechanical malfunctions. For instance, Thomas Edison wrote the following words in a letter to an associate in 1878: Baffle Ball, the first mechanical pinball game, was advertised as being 'free of bugs' in 1931. Problems with military gear during World War II were referred to as bugs (or glitches). In the 1940 film, Flight Command, a defect in a piece of direction-finding gear is called a 'bug'. In a book published in 1942, Louise Dickinson Rich, speaking of a powered ice cutting machine, said, 'Ice sawing was suspended until the creator could be brought in to take the bugs out of his darling.' Isaac Asimov used the term 'bug' to relate to issues with a robot in his short story 'Catch That Rabbit', published in 1944.