Nasdaq OMX Group Inc., under scrutiny after shares of Facebook Inc. were plagued by delays and mishandled orders on its first day of trading, blamed "poor design" in the software it uses for driving auctions in initial public offerings.

Computer systems used to establish the opening price were overwhelmed by order cancellations and updates as the "biggest IPO cross in the history of mankind" was occurring, Nasdaq Chief Executive Officer Robert Greifeld said yesterday in a conference call with reporters. 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 deal, he said.

While the errors were resolved and Facebook completed its offering, the day was another setback for equity exchanges trying to erase the memory of the botched IPO in March by Bats Global Markets Inc., another bourse owner. Nasdaq's issues contributed to disappointment among investors as Facebook's stock closed up 0.6 percent after rising 18 percent earlier.