Home > Backdoor

A backdoor in a login system could take the form of a hard-coded user and password combination which gives access to the system. A famous example of this was used as a plot device in the 1983 film WarGames, wherein the designer of a computer system (the 'WOPR') had inserted an undocumented password (named after his son) which gave the user access to the system and to undocumented aspects of its behavior (a video game like simulation mode).

An attempt to plant a backdoor in the Linux kernel, exposed in November 2003, showed how subtle such a code change could be. In this case a two-line change took the form of an apparent typographical error, which in practice gave the caller to the sys_wait4 function root access to the machine (see the external link below).

The prevalence of backdoors in proprietary software systems (those supplied without source code that can be inspected) is a topic of speculation, but they have been occasionally exposed in practice. Programmers have succeeded in secretly installing even large amounts of code as Easter eggs in programs without detection, though in these cases there may be official forebearance if not permission.

It is also possible to create a backdoor without modifying the source code of a program, or even modifying it after compilation. This can be done by rewriting the compiler so that it recognizes code during compilation that triggers inclusion of a backdoor in the compiled output. When the compromised compiler finds such code, it compiles it as normal, but also inserts a backdoor (perhaps a password recognition routine). So, when the user provides that input, he gains access to some (likely undocumented) aspect of program operation. This attack was first outlined by Ken Thompson in his famous paper Reflections on Trusting Trust.

Many computer wormA computer worm is a self-replicating computer program, similar to a computer virus. A virus attaches itself to, and becomes part of, another executable program; however, a worm is self-contained and does not need to be part of another program to propagats, such as Sobig and MydoomMydoom also known as Novarg Mimail. R and Shimgapi is a computer worm affecting Microsoft Windows. It was first sighted on January 26, 2004. It became the fastest spreading email worm ever (as of January 2004), exceeding previous records set by the Sobig, install a backdoor on the affected computer (generally a PCIBM PC compatible refers to a class of computers which make up the vast majority of smaller computers ( microcomputers) on the market today. They are based (without IBM's participation) on the original IBM PC. They use the Intel x86 architecture and are c on broadbandHardware Broadband is a type of transmission method where two or more signals share a medium. This is in contrast to a baseband transmission where one type of signal uses a medium's full bandwidth such as 100BaseT Ethernet. While people profess that narro running insecure versions of Microsoft WindowsImage use policy. Microsoft Windows is a range of commercial operating environments for personal computers. The range was first introduced by Microsoft in 1985 and eventually has come to dominate the world personal computer market. All recent versions of and Microsoft OutlookMicrosoft Outlook is a personal information manager and email client program from Microsoft, and is part of the Microsoft Office suite. Although often used mainly as an e-mail application, it also provides calendar, task and contact management. It can be). Such backdoors appear to be installed so that spammersSpam by e-mail is one type of spamming that involves sending identical or nearly identical messages to thousands (or millions) of recipients. Addresses of recipients are often harvested from Usenet postings or web pages, obtained from databases, or simply can send junk email from the machines in question.