The CESG website has an explanation [1]<p>[1] <a href="https:&#x2F;&#x2F;www.cesg.gov.uk&#x2F;articles&#x2F;problems-forcing-regular-password-expiry" rel="nofollow">https:&#x2F;&#x2F;www.cesg.gov.uk&#x2F;articles&#x2F;problems-forcing-regular-pa...</a>