Microsoft has landed a $500 million internet advertising account, signing Viacom to a 5-year deal, according to a Reuters report.

Microsoft, which vowed to become one of the top online ad companies in the next few years, replaces DoubleClick as Viacom's ad network. Microsoft also will sell remnant inventory across multiple sites for the media conglomerate.

Last week, Microsoft announced a similar ad deal to sell ads for CNBC.com, putting a little more heat on rivals Google and Yahoo! as all three look for ways to lock up content.