As of Tuesday's close, International Business Machines Inc. (NYSE:IBM) is down 25% month-to-date, putting the stock on pace for its worst month since December 1992.

That's worse than October 2018's 23% decline. Worse than September 2002's 22% drop.

And relative to the Nasdaq 100 index, IBM is underperforming by 23% this month, its weakest relative showing since February 2000.

The capitulation accelerated Monday, when IBM plunged 13% in a single session, its worst day since Oct. 19, 2000, at the peak of the dot-com bubble burst.

What Just Happened To IBM?

The selloff was triggered by a blog post.

Specifically, a post from AI startup Anthropic claiming that its Claude model can now analyze and interpret COBOL code, the decades-old programming language that still powers the backbone of global finance.

That claim struck at the heart of one of IBM's most durable businesses.

COBOL runs banks, insurance systems, airlines and government infrastructure. Roughly 95% of ATM transactions in the United States rely on it.

Hundreds of billions of lines of legacy code still operate ...