Lately there has been a rash of IPs hitting vbulletin sites for what ever reasons and most of them are Chinese IPs. I just helped another member here who was getting hit with tons of IPs and we blocked them through htaccess.
It is going to take a few hours of monitoring your site but you will get it under control. Here is the link to that member's thread :
https://vborg.vbsupport.ru/showthread.php?t=302628
If you need some help let me know, but it will require me to have access to your cPanel.