The share prices of Amazon and other major tech companies appeared to go haywire on the eve of the July 4 holiday after a market data glitch.

The confusion arose when some websites incorrectly showed Amazon (AMZN) plummeting 87%, Apple (AAPL) dropping 14% and Microsoft (MSFT) jumping 79% late Monday.

U.S. markets had closed early ahead of the holiday. But the crazy moves weren't the result of wild after-hours trading, according to Nasdaq, the exchange where the stocks are listed.

Nasdaq said the misleading prices came from test data it sent out that was "improperly" used by third party companies that supply information to websites.

Nasdaq is working with third party vendors to resolve the matter as quickly as possible. — Nasdaq (@Nasdaq) July 4, 2017

The bizarre numbers didn't affect actual trades in the stocks, Nasdaq spokesman Ryan Wells said.

If they had, the money involved could have been staggering. An 87% plunge in Amazon stock would have wiped nearly $400 billion off the company's market capitalization.

In the test data, Apple, Amazon and Microsoft's share prices were all listed as exactly $123.47. So were those of eBay (EBAY) -- a theoretical increase of 254% -- and video game developer Zynga (ZNGA) -- an implausible leap of 3,292%.

The erroneous prices showed up on the websites of CNNMoney, Bloomberg and Google Finance.

But they didn't appear on Nasdaq's own website, which showed the stocks' moves were far more muted in reality: Apple -0.4%, Amazon -1.5%, Microsoft -1.1%, eBay -0.9% and Zynga -0.6%.

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Nasdaq said the data that was sent out was part of "normal evening test procedures."

It urged third party data providers to switch back to its official closing prices that were effective at 5:16 p.m. ET.

By early Tuesday, the correct data was starting to appear on the websites affected.