A stock market data glitch set the share prices of some of the biggest companies swinging even after trading hours on Monday evening, Reuters reported. The prices were apparently only data distributed for routine testing by US stock exchanges at the end of each trading day, Financial Times reported.

However, some vendors used them as live figures, which led the numbers to go haywire on Bloomberg, Google Finance and Reuters. The changed prices did not reflect on the Nasdaq website.

While the prices of Amazon Inc and Microsoft Corp stocks plummeted by more than 50%, Apple’s shares rose 348% higher. Shares of online games group Zynga rocketed 3,000%, while Facebook’s remained unaffected.

The data glitch also reset the share prices of Amazon, Apple and Microsoft to exactly $123.47. The market value of Bed Bath & Beyond rose from about $4.4 billion to $17.9 billion.

Nasdaq said the “improper use of data” was being investigated, and that the actual prices of the stocks were not affected in this confusion, FT reported. “As part of its normal process, Unlisted Trading Privileges distributed test data, and certain third parties improperly propagated the data. Nasdaq is working with third-party vendors to resolve the matter.”