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

    LGI_BRK_TMO specifies the length of the failure monitoring
    period. This time increment is added to the suspect's expiration
    time each time a login failure occurs. Once the expiration period
    passes, prior failures are discarded, and the suspect is given a
    clean slate.

    LGI_BRK_TMO is a DYNAMIC parameter.