The stock market crash on Thursday afternoon took financial Web sites down with it, as people hurried online to make trades and check their investments.
Yahoo Finance, Fidelity.com and Google Finance are among the sites that people complained were unavailable or slow for a period during the afternoon.
A Yahoo spokeswoman would say only that Yahoo Finance experienced intermittent issues. Google said a small percentage of visitors may have experienced "sluggishness" for a brief period of time.
Fidelity said it saw near-record peak transaction volumes and had intermittent slowness but no interruption throughout the day. Some trades submitted online were executed but may not have been immediately visible to customers, said Vin Loporchio, a Fidelity spokesman.
Some people, including a few who wrote about their experience on Twitter, said the Fidelity site was unusable. "Your site not working cost me some serious $," wrote the Twitter user DerajFast.
Even more people on Twitter wrote about Yahoo Finance being inaccessible.
The Dow Jones Industrial Average dropped a massive 1,000 points on Thursday afternoon, a plunge that may have been caused by a trading error, according to some reports.
The incident led at least one lawmaker to call for better regulation over the technology behind stock trading. "I also have been warning for months that our regulators need to better understand high frequency trading, which appears to have played a role today when the US market dropped 481 points in 6 minutes and recovered 502 points just 10 minutes later," said Senator Ted Kaufman, a Democrat from Delaware, in a statement. "The potential for giant high-speed computers to generate false trades and create market chaos reared its head again today."