My scripts performs that feature and I found it was easier to store the words separately as items or as data with a reference number for the item.
You'll probably want to enclose the bad words/phrases with wildcards (i.e.: *hell* or *check out http* ) else it likely won't be detected unless it is the only word/phrase said to the channel.
Note on above: If you use an mIRC version before 6.03 it won't recognize the difference between 'W' and 'w' which results in a match when somebody types only an asterisk. This doesn't happen in v6.03
