Billions of spam emails are blocked every day, but to combat the smarter spammers, MSN and Hotmail have added new anti-spam tools

Microsoft on Thursday plans to unveil new anti-spam tools for its MSN and Hotmail services, noting that it now blocks 2.4bn email messages targeting subscriber in-boxes every day.

Microsoft said MSN 8 and Hotmail subscribers this week can elect to turn off images within emails, a feature that the company said would help cut down on spam. Images may conceal so-called "Web beacons" that confirm a particular email 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 anti-spam features to differentiate their products from rivals amid fierce competition for subscribers. AOL last week said it blocked about 2bn messages in a single day, while EarthLink on Wednesday announced a tough new "challenge-response" anti-spam tool.

According to spam-fighter Brightmail, unsolicited bulk mail volumes skyrocketed last year, now accounting for close to one-third of Internet traffic, up from just 8 percent in mid-2001.

The deluge is pushing companies to take more drastic steps to combat unwanted online marketing, including bringing lawsuits against suspected spammers and lobbying for laws that would establish tough penalties, including jail time for certain abuses.

On Wednesday, EarthLink won $16.4m (£10.2m) judgment against a spammer. Other suits are pending from Microsoft and AOL.

On the technology front, Microsoft and other Internet services have been steadily adding new anti-spam features and setting new policies to cut down on abuse.

In March, Microsoft began limiting Hotmail subscribers to sending only 100 messages a day, a measure aimed at curtailing spam abuses from its accounts.

Microsoft said it is seeing progress in attacking Hotmail account hijacking, as a program aimed at hindering spammers from using the service to ply their trade proves its worth. The company said it has seen a 20 percent drop in new account registrations since it inaugurated its human interactive proof (HIP) program in December.

HIP aims to stop bots from creating accounts by requiring applicants to complete steps that are difficult for a machine to accomplish. Microsoft said the drop-off in sign-ups shows that fewer spammers are securing accounts.

Other services, including Yahoo!, also offer similar image blocking and HIP anti-spam features.

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