User expire

The Drupal User expire module "allows an administrator to define a date on which to expire a specific user account or to define a period at a role level where inactive accounts will be locked."

http:BL

From the project page, "Implementation of http:BL for Drupal. http:BL can prevent email address harvesters and comment spammers from visiting your site by using a centralized DNS blacklist. It requires a free Project Honey Pot membership. This module provides efficient blacklist lookups and blocks malicious visitors effectively.

Security Kit

"Module provides Drupal installation with various security hardening options. This lets your mitigate the risks of exploitation of different web application vulnerabilities."