Why do a lot of hosts not allow IRC?

I think its cause of the EGGDROPS and BOTS taking large quantities of server resources.

Yep.

As I understand it some people try to take over a channel by killing the bot. To break it's hold over a channel they bombard it (essentially a DOS) until the link to the channel is broken. At this point it's up for grabs and their either just play with the channel, or set their own bot to mod it.

There may be other security problems too, but that's the thrust of it from what I've read around the net.

Greg Moore

Yes, generally speaking it is either because bots can use significant cpu power or because running an IRC server is like waving a big flag *and* walking around with a bullseye painted on your back.

I've helped out administrating a machine which runs an IRC service, and it usually got attacked at least once a day. Most attacks were small (~100 packets per second for 10 minutes) but at least once a week there would be a flood on the order of 1000 packets per second for half an hour or more. FreeBSD never had any trouble discarding all the packets, but it still clogged up the network and made the connection slow for everything else.