Both issues had been resolved, although Fidelity did not know the exact cause of the problems, company spokesman Jim Griffin said.
Customers were unable to access their accounts from 10:20 a.m. to 11:02 a.m. ET today because of authentication problems. Fidelity said that during that time investors could trade via telephone.
The watch list problem this afternoon perhaps was more troubling to customers. When clients tried to access stocks they are tracking, they instead received a portfolio belonging to another client of Fidelity's.
While the company said there was no "security breach," clients must enter their Social Security numbers and a pin number to access the watch list.
"But in no way shape or form did any customer get any other customers account data," said Griffen. "No customer data, including balances or positions, or anything else was breached by anyone else."
Online brokers in general suffer intermittent outages as the retail investors continue to migrate onto the Net. Just yesterday, Charles Schwab's online site crashed for the eighth time in four months. Most Net brokerages are moving to add server capacity to handle the growth in daily trades.