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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 . [http://www.computerweekly.com/Article23208.htm ETYMOLOGY Usage of the term "bug" to describe inexplicable defects has been a part of engineering jargon for many decades; it may have originally been used in hardware engineering to describe mechanical malfunctions. For instance, Edison wrote the following words in a letter to an associate in 1878 : ''It has been just so in all of my inventions. The first step is an intuition, and comes with a burst, then difficulties arise—this thing gives out and '' is '' then that "Bugs"—as such little faults and difficulties are called—show themselves and months of intense watching, study and labor are requisite before commercial success or failure is certainly reached.'' Problems with Radar electronics during World War II were referred to as ''bug''s (or glitches), and there is additional evidence that the usage dates back much earlier. The invention of the term is often erroneously attributed to Grace Hopper , who publicized the cause of a malfunction in an early electromechanical computer. A typical version of the story is given by this quote: ''In 1946, when Hopper was released from active duty, she joined the Harvard Faculty at the Computation Laboratory where she continued her work on the Mark II and Mark III. Operators traced an error in the Mark II to a moth trapped in a relay, coining the term ''bug''. This bug was carefully removed and taped to the log book September 9th 1945. Stemming from the first bug, today we call errors or glitch's {Link without Title} in a program a ''bug''. '' Hopper was not actually the one who found the insect, as she readily acknowledged. And the date was September 9 of 1947 , not of 1945 [http://americanhistory.si.edu/collections/object.cfm?key=35&objkey=30 . The operators who did find it were familiar with the engineering term and, amused, kept the insect with the notation "First actual case of bug being found." Hopper loved to recount the story. [http://www.jamesshuggins.com/h/tek1/first_computer_bug.htm] While it is certain that the Mark II operators did not coin the term "bug", it has been suggested that they did coin the related term "debug". PREVENTING BUGS It can be psychologically difficult for some engineers to accept that their design contains bugs. They may hide behind euphemisms like "issues" or "unplanned features". This is also true of corporate software where a fix for a bug is often called "a reliability enhancement". Bugs are a consequence of the nature of the programming task. Some bugs arise from simple oversights made when Computer Programmer s write Source Code carelessly or transcribe data incorrectly. Many Off-by-one Error s fall into this category. Other bugs arise from unintended interactions between different parts of a computer program. This happens because computer programs are often complex, often having been programmed by several different people over a great length of time, so that programmers are unable to mentally keep track of every possible way in which different parts can interact (the so-called '' Hrair Limit ''). Many Race Condition bugs fall into this category. The computer software industry has put a great deal of effort into finding methods for preventing programmers from inadvertently introducing bugs while writing software. These include: ; Programming techniques : Bugs often create inconsistencies in the internal data of a running program. Programs can be written to check the consistency of their own internal data while running. If an inconsistency is encountered, the program can immediately halt, so that the bug can be located and fixed. Alternatively, the program can simply inform the user, attempt to correct the inconsistency, and continue running. ; Development methodologies : There are several schemes for managing programmer activity, so that fewer bugs are produced. Many of these fall under the discipline of Software Engineering (which addresses software design issues as well.) For example, formal Program Specification s are used to state the exact behavior of programs, so that design bugs can be eliminated. ; Programming language support : Programming Languages often include features which help programmers deal with bugs, such as Exception Handling . In addition, many recently-invented languages have deliberately excluded features which can easily lead to bugs. For example, the Java Programming Language does not support Pointer arithmetic. DEBUGGING project data). A bug, submitted by the user, is ''unconfirmed.'' A reproduced bug is a ''confirmed'' bug. The confirmed bugs are later ''fixed''. Bugs, belonging to other categories (unreproducible, will not be fixed, etc) are usually in the minority]] ''Main article: Debugging '' Finding and fixing bugs, or "debugging", has always been a major part of Computer Programming . Maurice Wilkes , an early computing pioneer, described his realization in the late 1940s that much of the rest of his life would be spent finding mistakes in his own programs. As computer programs grow more complex, bugs become more common and difficult to fix. Often programmers spend more time and effort finding and fixing bugs than writing new code. Usually, the most difficult part of debugging is locating the erroneous part of the Source Code . Once the mistake is found, correcting it is usually easy. Programs known as Debugger s exist to help programmers locate bugs. However, even with the aid of a debugger, locating bugs is something of an art. Typically, the first step in locating a bug is finding a way to reproduce it easily. Once the bug is reproduced, the programmer can use a debugger or some other tool to monitor the execution of the program in the faulty region, and (eventually) find the problem. However, it is not always easy to reproduce bugs. Some bugs are triggered by inputs to the program which may be difficult for the programmer to re-create. One cause of the Therac-25 radiation machine deaths was a bug that occurred only when the machine operator very rapidly entered a treatment plan; it took days of practice to become able to do this, so the bug did not manifest in testing or when the manufacturer attempted to duplicate it. Other bugs may disappear when the program is run with a debugger; these are Heisenbug s (humorously named after the Heisenberg Uncertainty Principle .) Debugging is still a tedious task requiring considerable manpower. Since the 1990s , particularly following the Ariane 5 Flight 501 disaster, there has been a renewed interest in the development of effective automated aids to debugging. For instance, methods of Static Analysis by Abstract Interpretation have already made significant achievements, while still remaining much of a work in progress. FAMOUS COMPUTER BUGS The following is a list of famous computer bugs: Space Exploration
Medical
Computing
Telecommunications
Military
Video Games
MODERN BUGS AND SECURITY HOLES Traditionally bugs are fixed before a new release. In the first decade of the twenty-first century, as software becomes more complex, sometimes software is released with unknown bugs. Such bugs may just prevent the user from operating the software properly, but often they also produce:
In general, all Unverified software might have bugs. To find more about the number of known vulnerabilities a particular software may have at this moment, you can search for security bugs on the Secunia web page . COMMON TYPES OF COMPUTER BUGS
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