One common trick to cheat people to believe fake products or a high-return low-risk investment scheme in the online discussion groups is to make use of sockpuppets (i.e., use di erent fake identities pretending to be di erent persons to praise or create the illusion of support for the product). A fundamental problem is how to identify these sockpuppets. In this paper, we propose two approaches to identify these puppet pairs that occur in the same forum as well as cross forum. The evaluation based on millions of real posts in two popular discussion forums in Hong Kong shows that the methods are e ective.