A flood of traffic took down Charles Schwab & Co.’s website late Tuesday.

At approximately 3:45 p.m. EST, the brokerage’s website experienced a denial-of-service attack, which is essentially when hackers flood a website with traffic causing the server to become slow or crash.

The issue prevented Schwab’s brokerage customers from making trades as well as took the site offline for the general public. The company said phone access to its service professionals was available during the crash, although for a brief time immediately before market close call volumes were high.

The website was down for approximately one hour and forty minutes. Denial-of-service attacks have affected other financial institutions in recent years, including PNC, Bank of America and Wells Fargo,