Microsoft Monday officially rolled out two of its enterprise online subscription services that are focused around Exchange and SharePoint and said that it expects an explosion of users in the next five years.

Exchange Online and SharePoint Online give users a Microsoft hosted platform in the "cloud" as an alternative to deploying infrastructure locally. The Microsoft Online Services suite, available to companies of any size, is designed to give Microsoft a chance to beat back rivals muscling in on their enterprise software.

"In five years, we expect that 50% of Exchange and/or SharePoint seats will be services from Microsoft online," says John Betz, director of product management for online services.

The two services have been in beta since March and are the cornerstones of Online Services, a model that Microsoft had been incubating for more than three years.

The other services now include Office Live Meeting for conferencing and Microsoft Exchange Hosted Services for security, and will eventually include Microsoft Office Communications Online, a hosted version of Office Communications Server.

Microsoft also says it is developing a service that will enable IT to secure and manage desktops using a Web-based subscription. The company says the service would be based on existing systems management, identity and security offerings.

Those tools likely would include Systems Center Operations Manager and Configuration Manager, and the popular Microsoft Desktop Optimization Pack (MDOP), which gives users a number of inventory, deployment and management tools for desktops.

The service will be available early next year and will give "an IT person choices in how they consume our technology," said Betz. He would not provide details but he said Microsoft would eventually offer a number of infrastructure and desktop management services in "logical bundles" around the tools familiar to IT administrators today.

Microsoft officials said they would offer Exchange Online and SharePoint Online separately and in a bundle with the other services.

In July, the company said an information worker bundle will be priced at $15 per user per month and includes hosted versions of Exchange, SharePoint, Office Communications Server and Live Meeting.