As the User Name is the principal factor for identifying accounts upon log in, by definition, no two accounts can share the same User Name. IB enforces this constraint at the point of application by allowing the applicant to define the first 5 characters (lower-case letters) of the User Name and randomly assigning three trailing numbers which are then appended to the applicant-defined characters. Allowing the applicant to select these leading 5 characters is intended to strike a balance between enforcing unique User Names and providing a User Name that is easy to remember.
The User Name is required for log in to all account applications including Account Management, WebTrader and TraderWorkstation. Once established, the User Name cannot be changed and will remained associated with the account throughout its life.