The prices of several big-name Nasdaq-listed stocks appeared on some websites to either spike or plummet well after the closing bell on Wall Street yesterday.
This was seemingly due to a glitch related to the market data that runs the largely automated markets.
The prices of Amazon and Microsoft stocks appeared to have lost more than half their value, while Apple shares appeared to more than double.
Google parent Alphabet and eBay shares were among others that all appeared to be priced at $123.47 on some financial news websites.
The actual prices of the stocks were not affected and no trades were completed at that price, a Nasdaq spokesman confirmed.
Nasdaq said in a statement it was investigating the improper use of test data distributed by third parties.
Prices on Nasdaq's website were not affected.
Nasdaq and other US stock exchanges closed early yesterday ahead of the US Independence Day holiday today.
Testing of stock exchange software is mandated by the US Securities and Exchange Commission and happens on a regular basis to help prevent electronic glitches, often using test symbols and historical data.