Fizzer, technically known as W32/Fizzer@MM, W32.HLLW.Fizzer@mm, W32/Fizzer, W32/Fizzer-A, W32/Fizzer.gen@MM, Worm/Fizzu.A, and WORM_FIZZER.A, is a computer virus (specifically a worm and trojan) which spreads via e-mail to any Windows computer without AntiVirus software. It connects to several services, such as MSN, AIM, and IRC, in order to notify its creator of its existance on a computer.

When connecting to IRC, it has a list of 314 addresses it connects to. This list can be found on the Servers page. Fizzer connects using somewhat random nicknames, but uses a list of Names to make up its "real name" and ident.

After connecting to IRC, Fizzer joins a channel, which has mode +ilk, where the key is set to some sort of hash (since it's known by all of the Fizzers, but is not stored in the file anywhere). The channel names are also believed to be similar hashes. While in the channels, the "bots" say various random things in English and German.

There are many methods to help rid your IRC network of Fizzer. These are discussed on the FAQ page of this site.