I'm sure that they can, however its another issue for the Admin's to deal with.
To do that it would require an admin to be sat at the machine 24/7 if it were to be run effectively / effeciently. Now for obvious reasons thats just not possible, which means there will be time delays and large collections of users to accept which still wont necessarily stop the hackers / spammers from accessing the site.
The best thing that might be possible is using the IP address track back to the ISP and inform them of the issue, they may be able to do something for you, however this is a long shot unless what is being done is strictly illegal.