Adobe has announced that a patch to Acrobat and Reader, scheduled for release on Tuesday, September 9, will not be released until the week of September 15.
The update will include new versions of Reader and Acrobat for Windows and Mac. The new versions will address one or more critical vulnerabilities in the software, the exact nature of which remain unspecified for now.
The affected versions are Reader and Acrobat X 10.1.11 and earlier and Reader and Acrobat XI 11.0.08.
The company states, in an entry to the Adobe Product Security Incident Response Team (PSIRT) Blog, that the "...delay was necessary to address issues identified during routine regression testing." Delays like this are unusual, but not unheard of.
Corrected on September 10: Adobe provided advance notification of this update on September 4. An earlier version of this story stated that this was unusual for Adobe, but the company has been providing advance notification of their quarterly updates for Reader and Acrobat. Here is an example from May 8 of this year.