Nasdaq OMX Group Inc., under scrutiny after transactions involving shares of Facebook Inc. were plagued by delays and mishandled orders on the company’s first day of trading, blamed “poor design” in the software it uses for driving auctions in initial public offerings (IPO), Bloomberg reported.

Computer systems used to establish the opening price were overwhelmed by order cancellations and updates during the “biggest IPO cross in the history of mankind,” Nasdaq CEO Robert Greifeld said.

Nasdaq’s systems fell into a “loop” that prevented the second-largest U.S. stock venue operator from opening the shares on schedule following the $16 billion initial public offering (IPO).

Nasdaq’s issues contributed to disappointment among investors as Facebook’s stock closed up 0.6 percent after rising 18 percent earlier in the day May 18.

“This was not our finest hour,” Greifeld said after Nasdaq’s board convened to discuss the offering. Asked if his job is secure, he said, “I certainly hope so.”

Nasdaq will use an “accommodation pool” to pay back investors who should have received executions in the opening auction, based on the decisions of a third-party reviewer, Greifeld said.

That amount could total $13 million, he said.

Facebook advanced 23 cents to $38.23 on May 18 after surging as high as $45. The shares had slipped to $35 in early trading today, Bloomberg said.