Adobe has warned of a critical remote code execution vulnerability affecting Flash Player, Adobe Reader and Acrobat.
Hackers used the flaw in targeting "a very small number of organisations" and the attacks were "limited in scope," according to Adobe.
Attacks were seen in the wild using a corrupted Flash file, or SWF file, embedded inside a Microsoft Excel document sent out to targets.
It is possible the targets had their systems compromised.
"The .xls file is used to set up machine memory to take advantage of a crash triggered by the corrupted .swf file," Adobe's senior director for product security and privacy, Brad Arkin, said in a blog.
"The final step of the attack is to install persistent malware on the victim's machine."
This kind of structure is ideal for targeted attacks, said Kaspersky Lab expert Roel Schouwenberg, and questioned the need for Flash file embedding within Excel documents altogether.
"From my point of view, this is a clear example of too much functionality in a product leading to security problems," he added in a blog.
"As such, it would be great if Microsoft would allow us to turn off these excess features. Or, alternatively, Adobe could disallow such integration to reduce the attack surface."
As Adobe Flash is embedded in Adobe Acrobat and Reader, both of those software packages were affected as well.
Adobe said it would release a fix for Adobe Flash Player 10 and earlier versions for Windows, Macintosh, Linux, Solaris and Android during the week commencing 21 March.
That week will also see patches issued for the affected Acrobat and Reader software.
Adobe Reader X's sandboxing technology means it remained unaffected by the vulnerability as it could prevent the code from executing.
A patch for that software has been pencilled in for 14 June.
