ISPs and IP numbers

I moderate a forum for a national magazine in the UK and from time to time need to identify and ban trolls who multi-ID etc by trying to match IP numbers. We get little or no tech support from the magazine itself so I was hoping to get some simple (not too technical) info on here. I've had a quick look at the FAQs but can't see anything that matches my query. Apologies if I've missed it.

I believe that some ISPs allocate a unique IP number to each PC but that some, for example AOL, do not. So even an exact match of numbers would not necessarily mean it was the same PC. Is that right?

Where can I find out which ISPs have unique IP numbers, and which have ones which are shared, so when I look the IP address up I'll know if I'm getting a true match that will tell me if it's a multi-IDer?

[wimiadmin]

You can use our IP WHOIS Lookup tool to determine the "owner" of the IP and it will also show the block of IP addresses that are assigned to the same ISP.

Once you determine if the IP is coming from a country that primarily is known as spammers, like Nigeria, you can decide if you want to ban the single IP or the entire block.

I don't want to publicly show our banning methods, but I can say that we generally start off by banning the single IP first then if they come back under a similar IP, we'll ban the entire block.