• News/
  • https://www.theregister.com/2026/03/09/claude_legacy_code_vulns/

Microsoft Azure CTO set Claude on his 1986 Apple II code, says it found vulns

The Register
·
Tim Anderson
·
Published Mar 9, 2026
·
Updated

AI can reverse engineer machine code and find vulnerabilities in ancient legacy architectures, says Microsoft Azure CTO Mark Russinovich, who used his own Apple II code from 40 years ago as an example. Russinovich wrote: "We are entering an era of automated, AI-accelerated vulnerability discovery that will be leveraged by both defenders and attackers." In May 1986, Russinovich wrote a utility called Enhancer for the Apple II personal computer. The utility, written in 6502 machine language, added the ability to use a variable or BASIC expression for the destination of a GOTO, GOSUB, or RESTORE command, whereas without modification Applesoft BASIC would only accept a line number. Russinovich had Claude Opus 4.6, released early last month, look over the code. It decompiled the machine language and found several security issues, including a case of "silent incorrect behavior" where, if the destination line was not found, the program would set the pointer to the following line or past the end of the program, instead of reporting an error. The fix would be to check the carry flag, which is set if the line is not found, and branch to an error. Claude finds vulnerabilities in 40 year old type-in code for the Apple II The existence of the vulnerability in Apple II type-in code has only amusement value, but the ability of AI to decompile embedded code and find vulnerabilities is a concern. "Billions of legacy microcontrollers exist globally, many likely running fragile or poorly audite...

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Affected Software

2 affected components
Apple Apple II=May 1986
Anthropic Claude Opus=4.6
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Frequently Asked Questions

1

What is the main topic of this article?

The article discusses how an AI called Claude has been used to reverse engineer and identify vulnerabilities in legacy code from 1986.

2

Who demonstrated the AI's capabilities on legacy code?

Microsoft Azure CTO Mark Russinovich demonstrated Claude's capabilities by using his own Apple II code.

3

What significant issue is highlighted regarding legacy systems?

The article emphasizes that ancient legacy architectures may contain vulnerabilities that AI can identify and exploit.

4

What software products are specifically mentioned as affected by this vulnerability analysis?

The affected software includes the Apple II from May 1986 and Anthropic's Claude Opus version 4.6.

5

What are the potential security implications of AI reversing engineering legacy code?

The use of AI to analyze legacy code may lead to the discovery of previously unknown vulnerabilities that could be exploited.

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