Microsoft on Thursday plans to unveil new antispam tools for its MSN and Hotmail services, noting that it now blocks 2.4 billion e-mail messages targeting subscriber in-boxes every day.

Microsoft said MSN 8 and Hotmail subscribers this week can elect to turn off images within e-mails, a feature that the company said would help cut down on spam. Images may conceal so-called "Web beacons" that confirm a particular e-mail address is in use. That's important to spammers, who frequently use dictionary attacks that blanket domains with thousands of random variations in the hopes of hitting a handful of targets. Beacons can be triggered when images appear in a preview window, meaning recipients do not need to open the file to be painted as a target.

The announcement comes as online services are increasingly touting antispam features to differentiate their products from rivals amid fierce competition for subscribers. America Online last week said it blocked about 2 billion messages in a single day, while EarthLink on Wednesday announced a tough new "challenge-response" antispam tool.