Ah, now I understand.
Well, there's no single way to stop it. The measures you take depends on how skilled your hacker is.
Have you blocked his IP? Or if he uses multiple IPs, tried blocking an entire IP range? And for member flood of course, you can enable email validation and image confirmation (where you need to input the text from an image).
If you are a customer of Invision, why not upgrade to IPB 2.0.3 ? That is more secure as well. Also, I would suggest reading the documentation that comes with the download (in the ZIP) for basic security, and also reading in InvisionPower's own forums about security.
We can help you more if you tell what exactly is the hacker doing. More importantly, do you know WHO is trying to flood your board? If so, talk to him and try to solve the root cause of his enmity....
All the best

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