does your internet provider frequently change your IP address, or have you had the same one for a long time. If you changed IP recently, it's possible you have an address formerly used by someone infected.
Is there someone else in your LAN that's been accessing the same irc server, and it could be them instead of you that's infected?
Do you get this error at all irc servers you try to connect to? Your message makes it sound like you got this error at more than 1 irc server, but it would help if more of a warning error than 'compromised host'.
