Merge pull request kahun#128 from krondor/patch-5

Added SpamAssassin to Security Tools

Author: kahun

README.md

@@ -327,6 +327,7 @@ Comparison of NoSQL servers: http://kkovacs.eu/cassandra-vs-mongodb-vs-couchdb-v
 
 * [Denyhosts](http://denyhosts.sourceforge.net/) - Thwart SSH dictionary based attacks and brute force attacks.
 * [Fail2Ban](http://www.fail2ban.org/wiki/index.php/Main_Page) - Scans log files and takes action on IPs that show malicious behavior.
+* [SpamAssassin](https://spamassassin.apache.org/) - A powerful and popular email spam filter employing a variety of detection techniques.
 
 ## Service Discovery