Yahoo! has started a very aggressive anti spam measure. Every time you visit a chat room you need to put in the security code. This does NOT mean that once u have verified your id to be genuine (not spam or bot) you will not be asked again. Each and every time your visit a chat room you will have to do this. An alternative to this is Orca Chat.
By visiting Orca Chat at www.orcachat.blogspot.com you will always know that its a spam free chat room. You don't even have to register to chat. International chat with special room baised on region n topics.
Happy Chatting.