Microsoft has pushed back the re-release of a buggy Internet Explorer (IE) security update, saying that the quality of its software is still not up to snuff.

The critical update, originally released on 8 August, had been causing Microsoft's browser to crash while running some web-based applications. On Tuesday researchers disclosed that the software actually introduced a new critical vulnerability to IE.

Last week, Microsoft said it planned to re-issue the update, known as MS06-042, on Tuesday 22 August, but that date has now been pushed back indefinitely.

"Due to an issue discovered in final testing, Microsoft will not be re-releasing MS06-042 today," the company said on Tuesday in an advisory posted to its website. "This update will be re-released for Internet Explorer 6 Service Pack 1 when it meets an appropriate level of quality for broad distribution."

This advisory can be found here.

According to a source familiar with the matter, the delay is due to a problem in distributing the patch with Microsoft's Systems Management Server (SMS) product. The patch does work with the company's free update services, like Windows Update, the source added. "Obviously not everyone has bought [Microsoft's] SMS product and that shouldn't be a reason to delay patches," the source said.

Microsoft did add that it was investigating the reported security problem, discovered by eEye Digital Security Inc.

According to eEye, a bug in the MS06-042 patch could be used by attackers to run unauthorised software on a victim's PC. eEye discovered the security problem last week, and the company believes that the flaw also is known by other security researchers and exploit writers.

Last week, Microsoft released a "hotfix" download that addressed the patch flaws, but the company had hoped to re-release the entire update to ensure that all Windows users would automatically receive the new code.