The two most basis issues are:
The term is usually attributed to Captain (later Admiral) Grace Murray Hopper:
In 1945, while working in a World War I- vintage non-air-conditioned building on a hot humid summer day, the computer stopped. We searched for the problem and found a failing relay – one of the big signal relays. Inside, we found a moth that had been beaten to death. We pulled it out with tweezers and taped it to the log book. From then on, when the officer came in to ask if we were accomplishing anything, we told him that we were "debugging" the computer.[Quoted in Computerworld (November 16, 1981) and appearing in Morality and Machines by Stacey Edgar p. 293-4.]
Edgar mentioned that the term was used as long ago as 1889 by Thomas Edison. [Fred R. Shapiro, “The First Bug Exposed Byte 19 4 (April 1994)p. 308 and appearing in Morality and Machines by Stacey Edgar p. 293-4.]
Hardware problems – which can be caused by electrical system failures, power surges, “disk crash” and even (on rare occasions) faulty computer design. Failures of these types will usually result in data (and software) being lost and if these are critical systems (such as systems monitoring CCU patients and nuclear power plants), the results can be devastating. Most such problems rarely occur because redundancies are built into the systems to prevents (disk mirroring, data backups, UPS, etc.)
Data problems – These are caused by faulty programs or by errors in data transcription. This can include an error in how data or the program is stored in memory or on disk. While there are ways of detecting many errors (such as parity), they can’t spot all errors and they cannot correct most errors.
Software problems – The manner in which the program is designed and written to work is defective and results in the program not doing exactly what it is supposed to do.
Most errors that we are used to hearing are computer errors are usually human errors, caused either by the programmer or the data-entry clerk.
The Mars Climate Orbiter was to be the first weather satellite to ever orbit another planet. It would track the weather patterns and contents of the Martian atmosphere. More importantly, it was to be used as the primary relay station for the next two lander missions to come. However, as it approached the Mars orbit, a software error caused the Orbiter to enter much too low into the Martian atmosphere - within 36 miles of the ground, thus causing it to break apart and burn up. [http://www.dummysoftware.com/mars]
Therac 25 was engineered by Atomic Energy Canada Limited
(AECL) in conjunction with a French company CGR. It was an advancement in the fight
against cancer. The million dollar, dual-mode linear accelerator was first developed in
1976 and the commercial version was available in 1982. There were eleven installed
altogether, 5 in the USA and 6 in Canada. The machine precisely aimed a beam of radiation
at a patient to treat tumors caused by cancer. The x-rays produced were used to reach
deeper tissue in the human body. The machine had two settings, a low energy, 200-rad mode,
and a x-ray mode of 25 million electron volt capacity. The low setting could be directly
aimed at the patient whereas the high-energy mode had to aim at the patient through a
thick tungsten shield. It was controlled through a terminal hooked up to an old Vax
mainframe so that a technician could run it from another room.
In almost every case treatment went fine with no complications and it provided the
necessary radiation to cure the cancerous tumors. In six of the cases of people being
treated something went wrong. Human error, along with a bug in the software caused the
treatment to malfunction. Normally a patient is treated with low-energy doses of electrons
from Therac 25. It is the increased, high-energy x-rays that caused a problem. In each
case that Therac 25 malfunctioned, the technician entered the wrong dosage and then
corrected it.
The events that occurred around Therac 25 were the worst series of radiation accidents in
the 35-year history of medical accelerators. The deaths that occurred were unnecessary
and easily preventable if the time had been taken to properly test the equipment. The
FDA also concluded that software alone cannot be responsible for safety. Therac 25 was
an eye opener at the results of machinery put to work before it was ready and it had
deathly consequences.
While the idea of seems like a natural application, there are many problems with automated translations (see From English To English”)
Terry Dean Rogan, a Michigan man, was repeatedly listed by the
Nation Crime information Center as wanted for murder because another used his identity.
He was arrested erroneously 5 times starting in 1982, eventually sued and settled for
$55,000. Isaac Evans' arrest exemplifies the risks associated with computerization of
arrest warrants. Though his arrest was in fact warrantless—the warrant once issued having
been quashed over two weeks before the episode in suit—the computer reported otherwise.
Evans' case is not idiosyncratic. Rogan v. Los Angeles, 668 F. Supp. 1384 (CD Cal. 1987),
similarly indicates the problem. There, the Los Angeles Police Department, in 1982, had
entered into the NCIC computer an arrest warrant for a man suspected of robbery and murder.
Because the suspect had been impersonating Terry Dean Rogan, the arrest warrant erroneously
named Rogan. Compounding the error, the Los Angeles Police Department had failed to
include a description of the suspect's physical characteristics. During the next two
years, this incorrect and incomplete information caused Rogan to be arrested four times,
three times at gunpoint, after stops for minor traffic infractions in Michigan and
Oklahoma. See id., at 1387–1389.4 In another case of the same genre, the District Court
observed:
“Because of the inaccurate listing in the NCIC computer, defendant was a `marked man'
for the five months prior to his arrest.... At any time ... a routine check by the police
could well result in defendant's arrest, booking, search and detention…. Moreover, this
could happen anywhere in the United States where law enforcement officers had access to
NCIC information. Defendant was subject to being deprived of his liberty at any time and
without any legal basis.” U. S. v. Mackey (Nev. 1975).
Crazy billing stories are as old as the computer:
There have been many instances of elderly people whose pension and Social Security checks are deposited by direct deposit who have automatic deduction for rent, utilities and other payments, that continue for many weeks and even months after they die.
During 1960s to late 80s there was a widespread practice in all computer software to use two digits for representing a year rather than using 4 digits. This was done to save computer disk and memory space because these resources were relatively expensive in those times. As the year 90's approached experts began to realize this major shortcoming in the computer application software. In year 2000, the computer systems could interpret 00 as 1900 messing up all the computing work. For example if a program function is calculating difference between two dates, it would calculate a negative number. For example difference between 1 Jan 2000 and 31 Dec 1999 could be calculated as -100 years rather than 1 day. This was a major bug for the whole finance industry. The bug not only existed in computer software but it also existed in the firmware being used in the computer hardware. In general this bug threatened all the major industries including utilities, banking, manufacturing, telecom, airlines.
Y2K bug was a clicking time bomb for all major computer applications. The computer and system application companies came out with year 2000 compliant operating systems and system software. IT companies around the world spent billions of dollars to go through their entire application source code to look for the Y2K bug and fix it. Almost everybody raced around to make themselves Y2K compliant before the fast approaching deadline. Finally when the big day came, many utilities and other companies switched off their main computers and put the backup computers on work. When the clock ticked Jan 1, 2000, no major problems were reported. Almost every bank worked fine, no major power outages were reported, airplanes still flew and the whole world went on with its normal life.[http://www.y2ktimebomb.com]