Think Partnership has acquired Litmus Media and will incorporate the latter's pay-per-click search ad network, click-fraud prevention and shopping-cart abandonment prevention tools into its various interactive advertising companies - including the Kowabunga and Primary Ads affiliate networks and its MarketSmart Interactive paid search agency - ClickZ reports.

Think paid $6.5 million in cash and $6.5 million in stock up front. Litmus's management can earn up to $19.95 million more in cash and stock over the next three years.

Litmus runs the ValidClick Search Network, which provides PPC search advertising, local search advertising, shopping comparison and coupon content to search engines and web directories. It claims more than 1,000 search engine partners that process over 90 million searches per month. Litmus also operates online yellow pages, local city directories, a meta-shopping search engine, coupon search sites and an affinity-based search engine.

"As click fraud continues to artificially increase the cost of online advertising, erode the return on investment to advertisers, and continues to reach beyond search marketing into affiliate marketing and display advertising, we feel that Litmus's reliable solution to protect our advertising clients' investment is a key ingredient to being more effective in maximizing the ROI from their online advertising spend and provides us with a competitive, proprietary, competitive advantage in the marketplace," Scott Mitchell, president of Think Partnership, said in a statement.