Schwab CEO Walt Bettinger sent clients a letter apologizing for the inconvenience caused by thecompany’s website outage Tuesday. Bettinger also said another attack occurred Wednesday, intermittently slowing access to the firm’s website.

“These attacks did not involve unauthorized access to client accounts or client data. We sincerely apologize to each and every one of our valued clients and recognize how frustrating this situation is,” wrote Bettinger.

Bettinger added that he expects the attacks to continue in the future. “Based on the history of denial-of-service attacks on other companies, we anticipate these attacks may continue against our industry – and us – for some time. We will continue to work with the industry and law enforcement to ensure our websites are available without interruption.”