Google has announced that it is to purchase web-based security provider Postini for $625 million.

This buy-out will see Google's online applications increase to encompass Postini's security and encryption services, protecting instant messaging, e-mail and other communications.

Some industry experts are suggesting that this move will increase Google App's appeal to businesses and could be seen as a challenge to Microsoft.

Postinis's services are currently used by more than 35,000 businesses and 10 million users worldwide.

Google said the deal would let it provide companies with even more Web-based services similar to its Google Apps package, which currently includes the e-mail service Gmail, Calendar, and the messaging service Talk as well as Google Docs and Spreadsheets.

"With this transaction, we're reinforcing our commitment to delivering compelling hosted applications to businesses of all sizes", said Google chairman and chief executive Eric Schmidt.

"With the addition of Postini, our apps are not just simple and appealing to users - they can also streamline the complex information security mandates within these organisations."

If Google is closer than ever to a position where it can seriously take on Microsoft's Office package of applications, then this will possibly lead to renewed speculation that a Google OS is nearing fruition.