If you have been one of the lucky ones who have not received a email from a scam artist that starts off this way, you are one of the luck ones. They pose as people who have money and want your help to move it. However now they have taken it to the next level to bypass your spam filter, and that is on line chat.
It does not matter if it is Yahoo or some other service, you can expect someone posing as a person in need turning to the internet chats as a last resort. It is best to simply ignore them and block them. There is no special trick to it. Just keep in mind they are looking for a backdoor into your computer and hopefully your bank account. Never give out personal information.
Don’t even attempt to outsmart them as you have no idea what they are doing unseen. Most important never accept a file from them image or other. You acceptance may invite a Trojan or worm into your computer.
Just beware is the bottom line here!
Additional information http://en.wikipedia.org/wiki/Internet_fraud