NASDAQ technology stock exchange was "humbly embarrassed" by the glitches that had appeared during Facebook's first day of trading, the firm's Chief Executive Robert Greifeld told reporters Monday.

On Friday, the social network's much anticipated stock market debut was marred by technical glitches which caused the stocks to be trade more than half an hour late, with some investors being unable for hours to learn whether their orders had gone through.

Greifeld said that there was no indication that the delay contributed to the "underwhelming" performance of the stock which ended Friday's trading just 23 cents above the opening price at $38.23 (29.93 euros).

Calling Facebook's IPO "successful," Greifeld said that late order cancellations caused the glitch, and added that NASDAQ's board was planning to change its IPO auction process.

The United States' Securities and Exchange Commission said Monday that it was investigating the technical problems surrounding the IPO.

Market test

Facebook shares held steady Friday only with the help of underwriting banks which bought back shares to prevent the stock from plunging below its opening price of $38.

"I think that the underwriters convinced Facebook to offer too much stock," Wedbush Securities analyst Michael Pachter told AFP news agency, and added that the market didn't have enough "appetite" for such a large number of shares on offer.

Analysts now wonder what will happen to the stock when NASDAQ reopens Monday.

Mohannad Aama of Bream Capital Management told Reuters news agency that Facebook was likely to "fall below $38" as market conditions would worsen.

"Underwriters like Morgan Stanley will continue to defend the floor of $38. But this defense is not going to last endlessly," he said.

uhe/gb (Reuters, AFP, AP)