Today is not getting off to a good start for Yahoo.

NHN which owns both the South Korean equivalent of Google and the countrys largest gaming portal has decided to stop using the American companys advertising tech, and its chief didnt exactly have nice things to say when parting ways.Indeed, NHN CEO Kim Sang Hun stated according to Jun Yang, We desperately need an advertising platform thats more flexible and effective, with closer ties to the local market to respond to advertisers expectations promptly.Thats pretty harsh though in a businesslike and impersonal way. And making the matter worse for Yahoo is the fact that some investors seem to agree, sending NHNs stock up following the announcement.Now, whether other companies come around to that point of view or simply fall in line as a matter of following the leader, its not hard to imagine those comments could cause a sort of domino effect to take place.Jun Yang even wrote, Yahoos Overture may lose all its business in South Koreas 1 trillion won 836 million online advertising market as it is replaced with local technologies, said Choi Chan Seok, a Seoulbased analyst at KTB Securities.Anyway, Yahoos contract with NHN is set to expire later this year.