New members avoiding moderation-- Help

[Yago]

Please help me. I have 3 vbulletin forums and even though I have new member moderation checked on all of them, some still slip by and register as new members without giving me the opportunity to moderate. When I check users awaiting moderation, I see no one but when you check new registered users, I find them. Most of the time they are spammers.
Someone help me as this is begining to cause more headache than it is worth.
Thanks in advance.