Microsoft began pushing Service Pack 3 to owners of Office 2003 Thursday via its automated update service.

The automatic distribution had been pre-announced last month as part of a new policy that Microsoft introduced in December, when an Office product manager promised that the company would give users a 30-day warning before it seeded Windows Update with a service pack.

"Today marks the beginning of automatic distribution to [Microsoft Update] users," said an unidentified employee posting to the Microsoft Update (MU) product team blog. MU is a variant of the better-known Windows Update service; the former adds Office and other Microsoft software to the potential update pool.

"We've heard great feedback from customers who've already installed SP3 and feel confident in distributing it to the many users who rely on MU to keep their PCs secure, reliable and up to date," the post continued.

Not all users will receive notification via MU Thursday, the team added, since the update is being rolled out gradually. "Some users may see it install today, and for others, it may take a little longer," the blog read.

The service pack made news earlier this year when Microsoft acknowledged that new default security settings would block access to a wide range of older file formats, including several used in applications from rival Corel Corp. After users complained on the company's support forums, and Corel asked why its image file format was being barred, Microsoft apologized and posted work-arounds to make it easier for users to unblock the formats.

Office 2003 SP3 can also be downloaded directly from Microsoft's Web site.