A list of spam networks to block in Drupal if your website is US based only.

If your website users are only US based then you can use this list to assist in blocking users using the Xrummer software to create dummy user accounts on your system.
How to block malicious / spam networks with Drupal
Go to User Management and then select Access Rules. Add rule. First we block all mail with the extension of .ru. This is the Russian domain. You can do it with others but I found they are the the only ones spaming using their .ru extension. Amsterdam uses regular gmail accounts so I looked up the ips with www.arin.net and since my users are only US based no one from Amsterdam should be connecting to my site. Your list should look like this in the end. If anyone has any updates please use the comments button and submit your comment. Thanks and I hope this helps.

deny e-mail %@%.ru
deny host 212.%.%.%
deny host 87.%.%.%
deny host 150.%.%.%
deny host 93.%.%.%
deny host 89.%.%.%
deny host 213.%.%.%
deny host 85.%.%.%
deny host 86.%.%.%
deny host 90.%.%.%
deny host 91.%.%.%
deny host 78.%.%.%
deny host 79.%.%.%
deny host 8%.%.%.%
deny host 92.%.%.%
deny host 77.%.%.%
deny host 94.%.%.%
deny host 194.%.%.%
deny host 195.%.%.%
deny host 156.17.%.%.%
deny host 156.18.%.%
deny host 61.%.%.%
deny host 217.%.%.%
deny host 95.%.%.%
deny host 58.%.%.%
deny host 62.%.%.%
deny host 121.%.%.%
deny host 188.%.%.%
deny host 62.%.%.%
deny host 118.%.%.%
deny host 219.%.%.%
deny host 202.%.%.%
deny host 211.%.%.%
deny host 60.%.%.%