Adobe has patched a critical vulnerability in Adobe Reader, making good on a promise last week to plug the hole.

The company has also shipped a fix for Flash Player later today.

Last week, Adobe announced that attackers were exploiting an unpatched, or 'zero-day', vulnerability in Flash Player using malicious Microsoft Excel documents attached to email messages. At the time, Adobe said it would patch Flash, Reader and Acrobat sometime this week, but did not set a specific date.

Reader and Acrobat were also vulnerable because the same Flash flaw existed in the 'authplay.dll' component of those two programs. Authplay is the interpreter included in Reader and Acrobat that renders Flash content inside PDF files.

Adobe rolled out a patch for Reader and Acrobat around 7pm GMT, but said that the same fix for Flash would not appear until later in the evening.

Previously, Adobe said that while it has seen attacks exploiting the vulnerability via malformed Flash files embedded in Excel spreadsheets, it had not spotted any that targeted users with malicious PDF documents.

It's possible that cybercriminals could switch tactics, however, and exploit the bug by duping users into opening rogue PDF files.

"Keep in mind that even though we are currently only seeing exploits in the form of [Flash] files embedded inside [Excel] files and distributed via email, we are providing the fix across all configurations and platforms because there is always the possibility that an attacker could rework the exploit and use the vulnerability in another way," acknowledged Adobe spokeswoman Wiebke Lips.

Chrome users may not need to deploy any of today's patches because Google updated its browser - which includes an integrated copy of Flash Player - last week with the patch, said Adobe.

It depends on whether they're running Windows - and have a copy of Internet Explorer (IE) on their machine - said Lips today.

"If the user does have Internet Explorer and Flash Player [installed on that browser], in addition to Google Chrome with integrated Flash Player, the user would need to update Flash Player for Internet Explorer upon availability [of the patched version] this afternoon," said Lips.

Users can check whether Flash Player is installed in IE by pointing the browser to this Adobe page.

Adobe did not patch Adobe X, the newest version of the popular PDF viewer that includes an anti-exploit 'sandbox' designed to stymie most attacks. Adobe noted that Reader X's sandbox blocks the current attacks, and will also prevent malware from being installed if hackers switch to delivering the exploit in malicious PDFs.

Reader X's next quarterly update isn't slated until June 14.

The patched versions of Reader , Acrobat and Flash Player can be downloaded from Adobe's website. Alternately, users can run the programs' integrated update tool or wait for the software to prompt them that a new version is available.

See also: 21 years of Adobe Photoshop