Stock markets in the United States and especially in Europe took a hit on Thursday.
Markets in Europe dropped across the board, while Wall Street recovered most of its nerve at the opening of trading, with the Dow, Nasdaq and S&P 500 losing around half-a-percent.
So what is haunting the market?
The soundness of Portugal's largest bank, Banco Espirito Santo.
The tension centers on Espirito Santo International, the largest shareholder in Portugal's top-listed bank.
It allegedly missed a debt payment this week and was held responsible for accounting irregularities.
Amid the feeble pace of economic recovery in Europe, analysts say the shock in global stock markets shows that investors are still very worried about the overall financial health of the region.
That's also raising fears that Portugal might face a crisis again, just about a month after emerging from a bailout.
Portugal's regulator halted trading at the troubled bank after its share price crashed 17-percent.
The Portuguese government insists that its biggest bank is solid and that the drop in stock prices simply reflects trouble at the parent company.
Investors, however, are skeptical, saying they have heard such reassurances in Europe before and that the size of the problem remains unclear.
Hwang Ji-hye, Arirang News.