Microsoft has admitted that some of the source code for its widely used operating systems has been leaked on to the internet. BBC News Online explains what has happened and what the consequences will be.
What has happened?
The leak of Windows code is a huge embarassment
Some of the core computer code for Microsoft's Windows NT 4 and Windows 2000 products has been found circulating online. The files are reportedly proving very popular on file-sharing networks such as Kazaa and chat nets such as IRC.
What is source code?
It is the raw computer language written by programmers as they put together an application. When a program is compiled to become a working program this code is scrambled and becomes unreadable.
Commercial software firms guard source code for their products very carefully because rivals that get access to it could find out how their products work and copy them. A software company's source code is the equivalent to Coke's recipe for its fizzy drink.
What has been leaked?
So far there are only details about the leak of source code for Windows 2000, even though Microsoft has said that some of the code for NT4 is also online.
The Windows 2000 code is a 203MB chunk that expands to about 600MB - enough to fill one CD.
Microsoft has said that this represents about 15% of the total source code for the operating system. It is not enough to recreate the operating system.
The leaked chunk contains library and text files, scripts, executable programs and raw computer code. It seems to date from 25 July 2000.
Why is this a problem for Microsoft?
For several reasons.
Code for Windows 2000 and NT4 has been leaked
Firstly, it is yet another security lapse during a month that has seen the appearance of the fastest spreading virus ever as well as the discovery of yet another critical vulnerability in the Windows operating system.
Secondly, Microsoft's growth has come about because of its tight control of its intellectual property - the source code of its products. This has helped it maintain a stranglehold on the desktop computer market. That hold has been demonstrably loosened now. Rivals could use it to get a better idea of how Windows works and help them compete against Microsoft.
Thirdly, it might be the last straw for people tired of the security headaches that Windows creates.
Fourthly, for Microsoft to have this code paraded in public is hugely embarrassing. Not least because the code is littered with profanity and might show that many Microsoft programmers do not do a very good job.
In the past independent programmers that have deconstructed other Microsoft applications have been shocked at what they found within the code. Rivals and critics will be able to see exactly how Microsoft staff do their work.
Is this going to mean more security problems for Microsoft products?
It is too soon to say. Certainly knowing exactly how something works will be useful to anyone that wants to attack it, but few malicious hackers need an intimate knowledge of Windows to create havoc. Many of the viruses doing the rounds are simply copycat versions of older pernicious programs.
Virus writers tend to be lazy and build on the efforts of others. Few are likely to trawl through the millions of lines of code and go to the trouble of working out where new vulnerabilities can be found.
However, it just takes one dedicated vandal to do the work and the tools will be available to all
Microsoft has said it is more an intellectual property problem than it is a security issue.
Who has access to Windows source code?
Lots of people in thousands of organisations. Microsoft runs the Shared Source Initiative that lets researchers and key customers and business partners get a look at the basic code for many of its products. Up to 90% of the source code for Windows products has been shared over the years.
Windows XP builds on the leaked code
The only parts that Microsoft does not let anyone see are the bits dealing with product activation, its use of cryptography and code from other firms it cannot license directly.
This initiative was started to counter the success of the open source movement which is based around the freedom to inspect and play with the source code of computer programs.
Is this the first time this has happened?
It is the first leak of Windows source code though early releases of the various versions of Windows regularly circulate before they are official unveiled.
This leak is not thought to be related to the hack attack on Microsoft's corporate network that took place in October 2000.
Also, years ago code to version 6.22 of DOS was leaked online but no-one cared because it was so old.