Adobe has warned that its Flash product is under attack.
The announcement comes less than a week after it warned users that hackers were exploiting an unpatched bug in its Reader PDF viewer, Adobe said on Monday that Flash, its other prominent program.
The company said it would patch Flash in two weeks, and Reader in three weeks.
In a new security advisory on Monday, Adobe said that the current version of Flash contains a critical flaw already being used in the wild by criminals to attack Windows PCs. "This vulnerability could cause a crash and potentially allow an attacker to take control of the affected system," the advisory read.
The warning credited Steven Adair of the Shadowserver Foundation for reporting the vulnerability. Representatives of Shadowserver did not immediately reply to questions late Monday.
All editions of Flash, including those for Windows, Mac, Linux , Solaris and Google 's Android mobile operating system, include the flaw.
An Adobe spokeswoman characterized the attacks as "limited" and "targeted," and aimed only at Windows users.
The same bug is also present in Adobe Reader and Acrobat, the company's free PDF viewer, and its commercial PDF creation tool. That's not unusual, because both Reader and Acrobat include code to run Flash content embedded in PDF documents, making a bug in Adobe's media player typically require a patch for the PDF programs.
Adobe said it has no reports of attacks exploiting the Flash bug in Reader or Acrobat.
Monday's warning was the second since Sept. 8, when Adobe issued an advisory about a different unpatched, or "zero-day," vulnerability in Reader and Acrobat. Experts have said hackers began exploiting the Reader-Acrobat bug about the beginning of the month.
Those attacks have been dubbed "David Leadbetter" after the golf swing coach whose name was included in the subject lines of e-mails that included rigged PDFs. They have been called "scary" and "clever" for the way they sidestep important Windows defenses.
Adobe said it would update Flash to fix that program's flaw in two weeks, sometime during the week of 27 September.
The two bugs in Reader and Acrobat, the one disclosed last week and Monday's, will be patched in the week of 4 October with an emergency, or "out-of-band" security update.
Unlike Flash, Reader and Acrobat are supposed to receive updates on the second Tuesday of every third month. Adobe was to patch Reader and Acrobat on Oct. 12, but has ditched that in lieu of the rush update.
This will make two consecutive quarters that Adobe has had to abandon its usual patch schedule because of zero-day attacks. In late June the company released an emergency Reader update two weeks ahead of an already-slated July 13 update.
Reader's early October patch will also be its third rush fix in little more than three months.