what is a computer bug

what is a computer bug

A software bug is an error, flaw, mistake, failure, or fault in a computer program that prevents it from working as intended, or produces an incorrect result. Bugs arise from mistakes and errors, made by people, in either a program¡¯s source code or its design. A program that contains a large number of bugs, and/or bugs that seriously interfere with its functionality, is said to be buggy. Reports about bugs in a program are referred to as bug reports, also called PRs (problem reports), trouble reports, CRs (change requests), and so forth. 

Bugs can have a wide variety of effects, with varying levels of inconvenience to the user of the program. Some bugs have only a subtle effect on the program¡¯s functionality, and may thus lie undetected for a long time. More serious bugs may cause the program to crash or freeze. Other bugs lead to security problems; for example, a common type of bug which allows a buffer overflow may allow a malicious user to execute other programs that are normally not allowed to run.

The results of bugs may be extremely serious. A bug in the code controlling the Therac-25 radiation therapy machine was directly responsible for patient deaths and in 1996, the European Space Agency¡¯s US$1 billion prototype Ariane 5 rocket was destroyed less than a minute after launch, due to a bug in the on-board guidance computer program. Also, in June 1994 a Royal Air Force Chinook crashed into the Mull of Kintyre, killing 29. This was initially dismissed as pilot error, but an investigation by Computer Weekly uncovered evidence sufficient to convince a House of Lords enquiry that it may have been caused by a software bug in the aircraft¡¯s FADEC.