A flood of incorrect stock-market data briefly hit traders' screens around the globe early Tuesday morning in Asia, showing apparent huge moves in the Nasdaq-listed share prices of some of the world's biggest companies, including tech giants Apple Inc., Microsoft Corp. and Amazon.com Inc.
The faulty data on stock prices appeared on several platforms including Yahoo Finance, Google Finance and on Bloomberg terminals between 6 a.m. and 7 a.m. Hong Kong time, after U.S. markets Monday had closed early ahead of the Independence Day holiday.
As a result of the glitch, several stocks briefly showed their price to be $123.47 -- equivalent to a 14% drop in Apple's shares, an 87% plunge for Amazon and a 79% surge for Microsoft.
Joe Christinat, a Nasdaq spokesman, said no actual trades were affected by the glitch. Both normal trading and so-called after-markets trading, when investors can continue to trade via the exchange for a further four hours, had ended for the day on Nasdaq by the time the wrong data appeared.
If the stock price moves had actually occurred, it would have knocked $104 billion off the market value of Apple, the world's most valuable stock. Amazon's market cap would have dropped $396 billion, while Microsoft's would have risen $415 billion.
The appearance of the incorrect data sparked disagreement over who was to blame. A spokesman for Nasdaq said the problem was caused by test data being improperly disseminated by third-party vendors including Bloomberg.
However, a person familiar with one of the vendors said Nasdaq had changed its testing protocols but had not informed vendors ahead of time. Nasdaq said it had sent out a standard alert to the market on June 26 with the schedule for its data feeds for the early close on July 3.
A story that appeared early on Bloomberg's website Tuesday initially said a Nasdaq error had caused the faulty data. The story was later corrected to remove the reference to the Nasdaq error.
"This is a vendor issue, not a Nasdaq issue," said Nasdaq's Mr. Christinat, saying that others such as FactSet and even Nasdaq.com showed correct pricing data. That difference suggested that the faulty data issue was more the responsibility of some data providers.
In an emailed statement, a Google representative said, "We can confirm that our third-party finance data partner was providing some inaccurate information, which they received from Nasdaq."
"This is currently being fixed and we hope to update our stock price data shortly," Google said. According to the company's website, the closing prices on Google Finance are provided by SIX Financial Information and its intraday pricing data are provided by Interactive Data Real-Time Services. However, Google declined to confirm that those companies provide data to Google Finance.
A representative for SIX said its data feed wasn't the problem.
"We checked our data and it was correct," the representative said. "No incorrect prices came from us."
Apple, Amazon and Microsoft didn't respond immediately to requests for comment.
Stock markets in the U.S. were open for only a half-day session Monday and will be closed Tuesday in observance of Independence Day. Aftermarket hours on Nasdaq, during which shares trade following the close of the regular session, usually last for four hours. The market typically closes at 4 p.m. ET.
Nasdaq's Mr. Christinat said Monday's early close at 1 p.m. ET might have played a role in the confusion that prompted the improper use and dissemination of test data, which he said is sent out after every trading day.
"I've seen quite a few 'fat-finger' incidents when you get a funny price briefly," said Eric Moffett, a portfolio manager for the T. Rowe Price Asia Opportunities Equity Fund in Hong Kong. "When I saw the series of alerts, I figured something was up."
Mr. Moffett said he takes a long-term view on the stocks his fund invests in, so any sharp moves in the market -- whether from a fat finger or not -- likely won't prompt any significant trading activity. Even so, he said the flurry of alerts related to the pricing issues caught his attention.
"I immediately wondered with something like this if there was some sort of cyberattack," Mr. Moffett said.
Mr. Christinat at Nasdaq said he didn't see any evidence of a hack or a cyberattack affecting the erroneous pricing.
Several high-profile trading glitches have roiled markets in recent years. In August 2013, a technical glitch knocked out trading in all Nasdaq Stock Market securities for three hours due to a problem with the data feed that supplied trade information. In July 2015, a glitch forced the New York Stock Exchange to halt trading for nearly four hours.
Meanwhile, in May 2010, the Dow Jones Industrial Average plunged nearly 1000 points in a matter of minutes before rebounding quickly in what widely became known as the "flash crash."
The difference this time is that no trades appear to have been affected by the latest fiasco. A trader notice from Nasdaq said "certain third parties improperly propagated test data that was distributed as part of the normal evening test procedures." The notice added: "All production data was completed by 5:16 p.m. ET as expected per the early close of the markets. Any data messages received post 5:16 p.m. should be deemed as test data and purged from direct data recipient's databases."
A system status message posted on Nasdaq's website said "systems are operating normally." However, not all stock quotes appeared to be accurate. Shares in Nasdaq-listed biotech giant Amgen Inc. were still being incorrectly shown down 28% at $123.45 on Google Finance by late evening Asia time. The stock actually closed Monday at $172.80.
Amgen didn't respond immediately to a request for comment.