Google announced on Monday that the company had signed a definitive agreement to buy Internet messaging security firm Postini for $625 million in cash.

The acquisition would allow Google to offer e-mail and instant-messaging security as well as archiving and encryption services without requiring customers to purchase additional hardware. The offerings fit right into Google’s current line-up of hosted applications, such as GMail, Google Calendar and Google Docs & Spreadsheets, Dave Girouard, vice president of Google Enterprise, said in a statement.