Terms of the deal were not disclosed. Such deals are becoming more common as e-commerce expands.
"This investment will enhance our collaborative activities focused on delivering more powerful and profitable e-commerce solutions to Visa member banks and their customers," Visa International executive vice president Todd Chaffee said in a statement.
CyberSource develops commerce applications that include secure online payment and a fraud screening application. Consumers frequently mention security as a major concern when it comes to e-commerce.
Besides the equity investment, the two companies have begun exchanging data and expertise.
"CyberSource has worked closely with Visa over the last few months, and we are pleased to be recognized as a strategic partner," CyberSource chief executive Bill McKiernan said in a statement. The companies can work together in areas such as "shielding Web merchants and their banks from Internet credit card fraud," he added.
Founded in 1994, CyberSource is privately held.