Attempts to log onto Datek's Web site between 11:15 a.m. PT and 11:45 a.m. PT sporadically brought up a message that read: "Sorry, the page you tried to access is unavailable"
"The problem is being investigated but we did have some network problems," said Datek spokesman Michael Dunn. "It was limited but unfortunately we did have some difficulty today."
Customers unable to access the site were able to access the Iselin, N.J.-based trading company's brokers using its telephone service, the company said.
Even as online brokers add servers and capacity, trading sites are seeing their systems more frequently stressed, as people increasingly turn to online investing. Equity analysts recently noted a record number of accounts are being opened at Internet trading firms.
Earlier this month, DLJ Direct and Charles Schwab, both suffered downtime--with DLJ knocked out for two days in a row and Schwab twice during the month. In February, E*Trade and Datek both were victims of denial of service attacks.
In the early days of online trading, brokerage sites were more likely to go down on days that the markets fell sharply, as people logged on in droves to sell their positions.