As the clock ticks on support for mainstream Windows 2000 users, Microsoft has released a "high priority" update rollup of over 50 security fixes.

Rollup 1 for Windows 2000 SP4 was released Tuesday, just two days before mainstream support expires on June 30. The rollup contains fixes that were issued between the release of Windows 2000 SP4 and April 30, 2005. It contains a variety of fixes for files that have not been part of previous updates, so it should be applied even on systems that have been kept up to date, Microsoft said.

The rollup is listed as a "high priority" update on the Windows Update Web site, and will be placed under the "critical and service pack" categories. But Microsoft is transitioning Windows 2000 users to a new Windows Update site over the next few months, and the rollup will be listed there under the "critical and service packs" category, it said.

While Thursday marks the end of support for so-called mainstream Windows 2000 customers, the software maker also offers extended support until June 30, 2010, for a fee. All customers will receive free security hotfix support through March 31, 2010, however.

More information on the rollup is available on the company's Web site .