Microsoft on Tuesday revealed four vulnerabilities in the Mac version of its Office suite, but then failed to produce patches for the 2004 and 2008 editions.
Office for Mac 2011, which launched Oct. 26, was the only version updated as part of Microsoft's monthly Patch Tuesday.
Microsoft did not explain the omission of Office for Mac 2004 and Office for Mac 2008 patches, or say when it would ship updates for those editions.
"The security updates for Microsoft Office 2004 for Mac, Microsoft Office 2008 for Mac and Open XML File Format Converter for Mac are unavailable at this time," the company said in the accompanying security bulletin .
According to that bulletin, Office for Mac contains four vulnerabilities, all rated "important," the second-highest threat ranking in Microsoft's four-step scoring system. Microsoft confirmed that each bug could be used by attackers to infect a Mac with malware by labeling them with the phrase "remote code execution."
Along with a fifth bug, the same four flaws were patched Tuesday in all still-supported versions of Office for Windows.
On Windows, one of the five Office vulnerabilities lets criminals hijack a PC simply by sending a specially-crafted e-mail message. If the recipient opens the message or views it in Outlook's preview pane, "the game is over," one security expert said Tuesday.
It's not clear if the Mac versions of Office can be exploited in the same fashion; as is its practice, Microsoft provided no Mac-specific information in the security bulletin.
Although Microsoft advisories don't delve into technical details of vulnerabilities, they do provide some information, most notably that there are flaws in specific products. Hackers may be able to use that limited information as a starting point for probes into Office for Mac 2004 and Office for Mac 2008.
In the meantime, those versions remain vulnerable to attacks that have been blocked in Office for Mac 2011.
Microsoft also addressed several non-security bugs in the 14.0.1 update to Office for Mac 2011, including stability problems in Excel, compatibility issues in PowerPoint and message deletion troubles in Outlook.
This wasn't the first time that Microsoft revealed information that could be used by hackers to seize control of a computer before providing a patch.
In May 2009, Microsoft was criticised for shipping patches for the Windows version of PowerPoint but delaying fixes for the same flaws in the Mac software until the following month.
At the time, Microsoft's security team defended the decision in a post to the company's Security Research & Defense blog, saying there that it decided on the staged update -- Windows first, Mac second -- because fixes for the former were finished, but were still being tested on the latter.
Microsoft was not immediately available late Tuesday to answer questions about why it delayed the Office for Mac 2004/2008 updates, or when they would be released.