Users are distinguished by
(ident is always "Mibbit" if they use a Mibbit client on a webirc enabled server, the hostname or IP usually is cloaked), e.g.,
Those tripplets are called "hostmasks".
Many commands accept wildcards too, e.g.:
/mode #ch +b *!*bot@*80A677AE.IP
Hosts like 9C75DB05.72B5B948.80A677AE.IP are built of hashes from the user's IP, e.g.:
9C75DB05.72B5B948.80A677AE.IP representing a.b.c.d *.72B5B948.80A677AE.IP representing a.b.c.* *.80A677AE.IP representing a.b.*.*