AARD code
Encyclopedia
The AARD code was a segment of obfuscated machine code
that is included in several executables, including the installer and WIN.COM
, in a beta release of Microsoft Windows 3.1. It was a block of code which was XOR encrypted, self-modifying
, and deliberately obfuscated, using various undocumented DOS structures and functions to determine whether or not Windows really was running on MS-DOS. It was originally discovered by Geoff Chappell on 17 April 1992 and then further analyzed and documented in a joint effort with Andrew Schulman.
The AARD code ran several functional tests on the underlying DOS
that succeeded on MS-DOS
and PC-DOS
, but resulted in a technical support message on competing disk operating systems such as DR-DOS
. The name was derived from Microsoft programmer Aaron R. Reynolds (1955–2008), who used "AARD" to sign his work. ("AARD" was found in the machine code of the installer.) Microsoft disabled the AARD code for the final release of Windows 3.1, but did not remove it, so that it could have become reactivated anytime later by the change of a single byte in an installed system, thereby constituting a "smoking gun".
Digital Research
released a patch
to enable the AARD tests to pass on DR-DOS in 1992.
The rationale for the AARD code came to light when internal memos were released during the United States Microsoft antitrust case. Internal memos released by Microsoft revealed that the specific focus of these tests was DR-DOS
. At one point, Microsoft CEO Bill Gates
sent a memo to a number of employees, reading "You never sent me a response on the question of what things an app would do that would make it run with MSDOS and not run with DR-DOS. Is there [sic] feature they have that might get in our way?" Microsoft Senior Vice President Brad Silverberg
later sent another memo, stating: "What the [user] is supposed to do is feel uncomfortable, and when he has bugs, suspect that the problem is DR-DOS and then go out to buy MS-DOS."
Following the purchase of DR-DOS by Novell
and its renaming to "Novell DOS", Microsoft Co-President Jim Allchin stated in a memo, "If you're going to kill someone there isn't much reason to get all worked up about it and angry. Any discussions beforehand are a waste of time. We need to smile at Novell while we pull the trigger."
What had been DR-DOS changed hands again. The new owner, Caldera, Inc., began a lawsuit against Microsoft over the AARD code, Caldera vs. Microsoft, which was later settled. It was believed that the settlement ran in the order of $150m, but was revealed in November 2009 with the release of the Settlement Agreement to be $280m.
Obfuscated code
Obfuscated code is source or machine code that has been made difficult to understand for humans. Programmers may deliberately obfuscate code to conceal its purpose or its logic to prevent tampering, deter reverse engineering, or as a puzzle or recreational challenge for someone reading the source...
that is included in several executables, including the installer and WIN.COM
WIN.COM
WIN.COM is the executable file used to load versions of Windows that run from DOS. In Windows 3.1 and its predecessors, it is executed either manually from the DOS prompt or as a line in AUTOEXEC.BAT. In Windows 95 and onward it is automatically invoked by IO.SYS after AUTOEXEC.BAT is processed...
, in a beta release of Microsoft Windows 3.1. It was a block of code which was XOR encrypted, self-modifying
Self-modifying code
In computer science, self-modifying code is code that alters its own instructions while it is executing - usually to reduce the instruction path length and improve performance or simply to reduce otherwise repetitively similar code, thus simplifying maintenance...
, and deliberately obfuscated, using various undocumented DOS structures and functions to determine whether or not Windows really was running on MS-DOS. It was originally discovered by Geoff Chappell on 17 April 1992 and then further analyzed and documented in a joint effort with Andrew Schulman.
The AARD code ran several functional tests on the underlying DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
that succeeded on MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
and PC-DOS
PC-DOS
IBM PC DOS is a DOS system for the IBM Personal Computer and compatibles, manufactured and sold by IBM from the 1980s to the 2000s....
, but resulted in a technical support message on competing disk operating systems such as DR-DOS
DR-DOS
DR-DOS is an MS-DOS-compatible operating system for IBM PC-compatible personal computers, originally developed by Gary Kildall's Digital Research and derived from Concurrent PC DOS 6.0, which was an advanced successor of CP/M-86...
. The name was derived from Microsoft programmer Aaron R. Reynolds (1955–2008), who used "AARD" to sign his work. ("AARD" was found in the machine code of the installer.) Microsoft disabled the AARD code for the final release of Windows 3.1, but did not remove it, so that it could have become reactivated anytime later by the change of a single byte in an installed system, thereby constituting a "smoking gun".
Digital Research
Digital Research
Digital Research, Inc. was the company created by Dr. Gary Kildall to market and develop his CP/M operating system and related products. It was the first large software company in the microcomputer world...
released a patch
Patch (computing)
A patch is a piece of software designed to fix problems with, or update a computer program or its supporting data. This includes fixing security vulnerabilities and other bugs, and improving the usability or performance...
to enable the AARD tests to pass on DR-DOS in 1992.
The rationale for the AARD code came to light when internal memos were released during the United States Microsoft antitrust case. Internal memos released by Microsoft revealed that the specific focus of these tests was DR-DOS
DR-DOS
DR-DOS is an MS-DOS-compatible operating system for IBM PC-compatible personal computers, originally developed by Gary Kildall's Digital Research and derived from Concurrent PC DOS 6.0, which was an advanced successor of CP/M-86...
. At one point, Microsoft CEO Bill Gates
Bill Gates
William Henry "Bill" Gates III is an American business magnate, investor, philanthropist, and author. Gates is the former CEO and current chairman of Microsoft, the software company he founded with Paul Allen...
sent a memo to a number of employees, reading "You never sent me a response on the question of what things an app would do that would make it run with MSDOS and not run with DR-DOS. Is there [sic] feature they have that might get in our way?" Microsoft Senior Vice President Brad Silverberg
Brad Silverberg
Brad Silverberg is most noted for his work at Microsoft in 1990–1999 as Senior VP and product manager for MS-DOS, Windows, Internet Explorer, and Office...
later sent another memo, stating: "What the [user] is supposed to do is feel uncomfortable, and when he has bugs, suspect that the problem is DR-DOS and then go out to buy MS-DOS."
Following the purchase of DR-DOS by Novell
Novell
Novell, Inc. is a multinational software and services company. It is a wholly owned subsidiary of The Attachmate Group. It specializes in network operating systems, such as Novell NetWare; systems management solutions, such as Novell ZENworks; and collaboration solutions, such as Novell Groupwise...
and its renaming to "Novell DOS", Microsoft Co-President Jim Allchin stated in a memo, "If you're going to kill someone there isn't much reason to get all worked up about it and angry. Any discussions beforehand are a waste of time. We need to smile at Novell while we pull the trigger."
What had been DR-DOS changed hands again. The new owner, Caldera, Inc., began a lawsuit against Microsoft over the AARD code, Caldera vs. Microsoft, which was later settled. It was believed that the settlement ran in the order of $150m, but was revealed in November 2009 with the release of the Settlement Agreement to be $280m.
External links
- AARDvarks in your code
- So why didn't the Windows guys just remove the AARD code from the system?
- Details and initial discovery (archived site)
- Caldera v. Microsoft details
- Site with email excerpts from Microsoft and an example of tripping the AARD code (XMS error)