But it has happened.
CBS News Correspondent Wyatt Andrews reports on how banks and brokerages are fighting a daily battle against hackers -- and preparing for all-out war.
For all the inconvenience the hack attackers caused this week, they did not steal any money or rob any banks.
But it's not as if they don't try.
Catherine Allen runs a consortium of 100 banks and brokerage firms that have joined to fend off the daily hacking assault on the banking system. They do it by trying to outsmart the hackers.
"We estimate anywhere from 100 to 1,000 attacks every day," she says.
"We try to hack ourselves, and most financial institutions employ 'ethical hackers' as well, to try to hack themselves," added Allen.
|Click here for Online Security Tips for Consumers of Financial Services from the Banking Industry Technology Secretariat (BITS).|
They then tell the banks how they got in, how much they stole and how the gaps in software security can be closed. The industry also traces, in real time, any attempt to hack a bank's computer.
"The bank robbers of the past used guns, the bank robbers of the future use the Internet," says Allen. "We're all vulnerable who are involved in e-commerce," she adds.
Michael Vatis, of the FBI, tracks the rising number of criminals who hack for money. He says, "The problem is, we're in a race with the bad guys."
"Their skill and their knowledge is increasing very quickly and it's imperative that security be speeded up to respond to the threat," he added.
When you consider credit card purchases, ATMs, online banking and online stock trades, computer networks now handle 100s of billions of dollars. It's where the money is.
So, E-Trade and Yahoo suffered nuisance attacks this week, but the high stakes online war to protect your credit cards and money is being waged every day.
For more information on computer intrusions and computer crime, go to the FBI Web site.