Security software vendor Webroot plans to acquire Email Systems, a provider of e-mail and Web protection services.

The acquisition, which is set to be announced on Tuesday, will give Webroot a new line of "software as a service" (SaaS) products to complement its existing security software. Webroot sells a popular anti-spyware program called Spy Sweeper.

Based in Westerham, UK, Email Systems sells e-mail, Web and data archiving management services. The company also has offices in France, Sweden, Holland and Australia, and its services are used to manage 2.5 million mailboxes.

Following the acquisition, Webroot will sell Email Systems' Web-based services under the brand name Webroot Email Security SaaS, a representative from Webroot's public relations agency wrote in an e-mail disclosing the planned acquisition, sent late Monday.

"Webroot Email Security SaaS will be an important piece to the layered security approach by offering levels of network protection beyond what an on-premise solution can provide," the spokesman wrote.

More details on the purchase are set to be disclosed on Tuesday morning, he added.