An automated stock-trading program accidentally flooded the market with millions of trades Wednesday morning, spreading turmoil across Wall Street and drawing renewed attention to the fragility and instability of the nation’s stock markets.

While the markets quickly recovered, it was the latest black eye for the financial markets and suggests that regulators have not been able to curb the market disruptions that have led to frequent halts in trading and wild swings in shares.

Wednesday’s debacle follows the botched Facebook initial public offering on Nasdaq in May and the aborted effort by another exchange, BATS Global Markets, to bring its own stock public on its own exchange. The episodes have further rattled the confidence of investors and stoked suspicions that markets are unsafe for savings.

‘The machines have taken over, right?