Block Reserved Usernames
Prevents anyone from registering or being created with usernames like admin, support or root that look official or invite attacks.
Snippet Library
Users snippets for WordPress
Snippets for user accounts, roles and profiles: extra profile fields, new columns in the users list, last-login tracking and tighter control of what each role can do. Handy for membership sites, client sites and teams with many authors.
Require Unique Display Names
Stops users from picking a public display name that another member already uses, which prevents impersonation in comments and forums.
bbPress: Stop Replies to Old, Inactive Topics
Hides the reply form on topics with no activity for a set number of days and shows a note instead, which prevents necro-posting and old-thread spam.