我的一个网站收到了大量的注册垃圾邮件。我在注册表上有一个Captcha和一个数学问题，但它似乎没什么帮助。我是否可能遇到手动垃圾邮件发送者或我的预防机制不够好？
注册表格在这里：
http://peaksoverpoverty.org/wp-signup.php
更新
我过去一周一直在跟踪行为，这是访问日志中的典型请求：
174.132.130.194 - - [18/Jan/2011:07:24:55 -0600] "GET / HTTP/1.1" 302 20 "http://peaksoverpoverty.org/wp-signup.php" "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET CLR 3.0.04506; Media Center PC 5.0; SLCC1; Tablet PC 2.0)"
稍微调整一下后，用户代理字符串看起来不一定是恶意的 - this tool能够解释整个字符串。然后，我再也没有真正盯着用户代理字符串了很长时间。我知道他们很容易被欺骗，但这就是垃圾邮件发送者所发送的内容。
此外，这是我过去一周收集并阻止的违规IP地址列表：
174.120.203.66
174.120.245.194
174.122.107.138
174.122.175.162
174.123.101.98
174.132.130.194
174.142.241.137
175.41.168.169
184.154.74.21
187.63.208.241
195.56.42.131
199.16.130.53
200.17.56.7
201.22.130.66
201.59.175.2
201.59.175.29
205.186.184.10
208.100.27.143
208.100.27.154
208.100.27.159
208.100.27.186
208.101.30.165
208.43.73.29
209.151.224.235
209.151.224.240
212.227.119.47
213.251.189.204
213.251.189.205
216.108.225.220
216.108.225.242
220.181.94.212
222.237.79.242
24.252.62.57
62.215.5.66
64.22.89.70
66.172.42.11
66.232.112.144
66.232.112.168
66.249.71.217
66.96.219.38
67.109.124.170
67.18.19.194
67.18.5.2
67.18.72.2
67.225.184.5
69.117.20.174
69.117.22.237
69.117.24.21
69.117.26.195
69.147.240.90
69.147.249.161
69.147.249.22
69.147.249.99
69.167.175.27
69.28.58.35
69.56.228.130
69.89.31.240
71.208.210.208
72.18.157.147
74.220.215.68
74.53.28.2
74.54.131.82
74.54.95.210
77.235.37.41
79.125.33.136
79.172.242.144
80.252.171.68
82.80.235.146
84.16.243.243
85.17.199.46
85.214.92.15
85.92.83.164
86.196.41.15
86.208.68.211
88.191.126.212
88.208.33.130
90.18.14.167
90.47.218.215
90.59.74.139
91.121.203.226
91.184.49.210
91.207.254.234
93.174.95.153
94.125.27.20
95.133.38.238
攻击者似乎提供了相当动态的IP地址。任何进一步的想法都会很棒。我真的开始认为这些都是人工攻击，但仍然不能100％肯定，因为我从来没有处理过这么糟糕的垃圾邮件问题。