Purchase of online ad firm will help Yahoo extend its reach as it continues to challenge rivals Google and Microsoft Yahoo continued its pursuit of online ad rivals with a $300 million purchase of private online advertising firm BlueLithium, the Internet giant announced Wednesday.San Jose, California-based BlueLithium offers banner advertising on a network of about 1,000 sites, which will help to extend Yahoo’s ad reach as it continues to challenge rivals Google and Microsoft’s online ad offerings.The deal is for cash and is expected to close at the end of the fourth quarter of 2007, Yahoo said. BlueLithium will become a Yahoo subsidiary once the acquisition is completed. It will be integrated with other Yahoo ad offerings, including the Yahoo Publisher Network and the Right Media Exchange. Increased competition in the online advertising market between Yahoo, Microsoft, and Google has led to a series of acquisitions by all three companies. Yahoo has struggled over the past year, reporting disappointing second-quarter financial results and a decrease in net income over the same period in 2006. The company has also spent almost a year reorganizing both its top management and its business divisions. Software DevelopmentTechnology Industry