A press release announcing that Pfizer (PFE) would no longer increase the prices of its drugs began circulating Thursday afternoon—a seemingly watershed decision in the pharmaceutical industry, which for months has faced intense scrutiny of its drug price hikes and accusations of price-gouging.

Alas, the announcement, as well as a website it linked to pfizerinternational.com, turned out to be fake. Pfizer denied association with the “anonymously issued” press release and website in its own statement a few hours later, saying “it was erroneously attributed to Pfizer and should be disregarded.” Both the website and the false release have apparently since been removed, and Pfizer said it was investigating the incident and could pursue legal action.

It wasn’t clear whether the perpetrators of the prank were trying to manipulate Pfizer’s stock price, or merely playing a trick on the company, perhaps to celebrate April Fool’s Day. The scheme was reminiscent of recent stock manipulation scams where fraudsters filed bogus SEC filings about Warren Buffett’s stock purchases and takeover offers in an attempt to pump up stock prices for their own gain.

But at least one news outlet fell for the hoax, with the Washington Post publishing a story headlined, “Pfizer vows to stop raising the list prices of its drugs.” (The newspaper removed the story after it was revealed to be false.)

Investors, however, were not so gullible. Pfizer’s stock price fell only 2% after the hoax came out—a minor dip for an announcement that implied Pfizer was giving up one of its key tools for preserving profit margins—and soon recovered, closing the day down 1.4%.

One market analysis firm, Connecticut-based Hammerstone Group, warned its hundreds of clients at 2:46 p.m to beware that the drug pricing announcement was fake. “**CAREFUL xxxxx,” it wrote in an alert to traders and investors.

Others expressed their incredulity and outrage at the scam on Twitter:

Pharmaceutical giant Pfizer vowed today to stop the time-tested habit of jacking up the list price of its drugs https://t.co/Bqe1av1GAb

— rasi (@twisira) March 31, 2016

https://twitter.com/EricDubowsky/status/715616345715511296

$PFE talks about fake website… we alerted subs at 2:46PM to be aware it was fake

— Jamie Lissette (@jamielissette) March 31, 2016

As Idiot Day approaches, 4/1, it's time to end prank PR releases, i.e., the WP on Pfizer. https://t.co/spS8gpB4VT

— justinbachman (@justinbachman) March 31, 2016