Questions have been raised over the effects on the markets of the rogue trader who lost 4.9bn euros ($7.1bn; £3.7bn) at Societe Generale.
Jerome Kerviel, the reported rogue trader
Analysts are trying to assess whether the trader's actions contributed to the stock market turmoil and the Fed decision to cut interest rates.
They also say that the losses have left the bank vulnerable to a takeover bid.
While the French bank has yet to name the trader, media reports say he is 31-year-old Frenchman Jerome Kerviel.
"Societe Generale will certainly lose its independence after such an operation. We will... have a redefinition of the banking world and France will be no exception," Alain Crouzat at Montsegur Finance told Le Parisien newspaper.
'Large-scale internal fraud'
French Prime Minister Francois Fillon said on Friday that the French government was notified about the fraud on Wednesday, though the bank had uncovered it several days earlier.
"Maybe the government should have been told earlier," he said.
French President Nicolas Sarkozy called the events at Societe Generale a "large-scale internal fraud", but added that the losses "do not affect the solidity and reliability of the French system".
Societe Generale chairman Daniel Bouton said the fraud was a "one-off" and denied it was a trading or risk-management fault.
The bank has filed a legal complaint against the trader accused of defrauding the bank which led to a loss of 4.9bn euros ($7.1bn; £3.7bn).
'Fuelled the nerves'
SOCIETE GENERALE IN FIGURES
Founded in 1864
467bn euros in assets under management (as of June 2007)
22.5m customers worldwide
120,000 employees in 77 countries
Some analysts suggest that the rogue trader's actions might have contributed to a dramatic fall in many stock indexes earlier this week.
"Something like this can aggravate the situation, but there has to be underlying concern in the first place," said Howard Archer, economist at Global Insight.
"Any market that is nervous for a number of reasons is going to be touchy. And anything that adds fuel to the nerves isn't going to help," said Anthony Scott, a stockbroker at Charles Stanley.
Meanwhile, a source from the US Federal Reserve said on Thursday that the Fed was not aware of the fraud at Societe Generale when it made a decision to slash interest rates at the beginning of the week.
'Apologies and regrets'
Newspapers published on Friday Mr Bouton's full-page advertisements, in which he asked the bank's shareholders to accept his "apologies and deep regrets".
"I understand your disappointment, your anger. This situation is perfectly unacceptable," he wrote.
"I am aware of what the drop in the share price means for you," added the bank's chief executive.
Societe Generale's shares, which ended the previous trading session down 4.1%, were up 2.1% in afternoon trade on Friday.
They have fallen by nearly 50% in the past six months.
The bank said the fraud was based on simple transactions, but concealed by "sophisticated and varied techniques".
SOME MAJOR BANK FRAUDS
2008: Societe Generale, alleged fraud by a trader, 4.9bn euros loss
2002: former currency trader accused of hiding $691m in losses at Allfirst bank of Baltimore
1995: UK's Barings Bank collapsed after a trader Nick Leeson lost £860m ($1.28bn at the time) on futures trades
The trader responsible for the fraud had "in-depth knowledge of the control procedures resulting from this former employment in the middle-office", the bank said.
According to reports, Mr Kerviel worked at the bank's Delta One products team in Paris.
He was responsible for betting on the markets' future performance, bank executives said.
Societe Generale said the trader had taken what it called "massive fraudulent directional positions in 2007 and 2008 beyond his limited authority".
Executives said the trader may not have sought personal gain from the fraudulent deals.
Scale of the fraud
The losses are four times greater than those made by Nick Leeson, the rogue trader who brought down Barings Bank.
Leeson was sentenced to six-and-a-half years in jail.
Speaking to the BBC, Leeson said he was not shocked that the latest fraud had taken place - only by its scale.
"I never for one moment believed it would get to this degree of magnitude, this degree of loss," he said.
The bank, one of France's largest, has arranged a rights issue worth 5.5bn euros in new capital in order to offset the losses.
But it said it would still make a profit of 600m to 800m euros for 2007, despite the blow to its balance sheet.