Bank of America's website returned to normal on Wednesday, but not until customers had endured a full six days of error messages and excruciatingly slow service. The problems started suddenly, and mysteriously, a day after the bank announced a hugely unpopular $5 debit card fee last week. Many customers were already threatening to switch banks over the new fee — now they're really seething. Bank of America denied it had been attacked by hackers, but offered only foggy explanations for days. Here, a brief guide to the ordeal:

Why are Bank of America customers so mad?
The duration of the bank's online problems was "unprecedented," says Shawn White, a vice president for web-monitoring service Keynote Systems, as quoted in ComputerWorld. It's "shocking" that brownouts and slowdowns — taking up to a minute to complete a simple transaction  persisted as long as they did, he said, as the bank knows customers depend on its site to make payments. And the bank's failure early on to say why the site was slow didn't help. Bank of America has been looking into the root of the problem, said spokeswoman Tara Burke. "We're not going to get into the technical details."

What made people suspect hackers?
Mainly the "absence of a fuller explanation," says Martha C. White of TIME. The symptoms suggested a denial-of-service attack — a barrage of traffic aiming to overload a website's servers. Such attacks are potentially crippling, but relatively simple to engineer. "The only reasonable conclusion is that they are under attack," said internet security expert Steve Gibson. "A site of that size should be expected to handle huge volume with no trouble at all."

Is there any other explanation?
On Thursday morning, Bank of America's head of mobile and online banking, David Owen, said the company was adding new features while also facing heavy month-end traffic. The bank consulted police and outside experts, and turned up no evidence of hackers. "There is nothing that points to a third-party intervention," Owen said. Some people believed that a January outage on the website was the result of an attack by WikiLeaks advocates "Anonymous," a suspicion fueled after WikiLeaks founder Julian Assange hinted that the whistle-blower site's next leak would target a large bank. That outage, however, was eventually blamed on a glitch in a routine system change. 

Sources: ComputerWorld, TIME, ABC News, Huffington Post, CNN