/sys$common/syshlp/helplib.hlb Sys Parameters, LGI_BRK_LIM  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    LGI_BRK_LIM specifies the number of failures that can occur at
    login time before the system takes action against a possible
    break-in. The count of failures applies independently to login
    attempts by each user name, terminal, and node. Whenever login
    attempts from any of these sources reach the break-in limit
    specified by LGI_BRK_LIM, the system assumes it is under attack
    and initiates evasive action as specified by the LGI_HID_TIM
    parameter.

    The minimum value is 1. The default value is usually adequate.

    LGI_BRK_LIM is a DYNAMIC parameter.