Security Plugins:
iThemes Security (formerly Better WP Security)
Exploit Scanner – just scanning
WPScan – black box WordPress vulnerability scanner (not plugin)
Articles:
How to Secure WordPress Website
How to Clean a Hacked WordPress Site
How to Clean a Hacked WordPress Site
Hacking WordPress Sites on Shared Servers
How to Identify and Fix a Hacked WordPress Website
How to Find a Backdoor in a Hacked WordPress Site and Fix It