Adobe has urged users of its Flash Player plug-in to install an update to protect themselves against the risk of hackers hijacking their PCs.
It cited a "critical vulnerability" in older versions and said it had become aware of reports that cybercriminals had worked out a way to exploit it.
A new version of the multimedia player has been made available for download for Windows, Mac and Linux computers.
This is the latest in a series of setbacks for the company.
The California-based software maker acknowledged that usernames and encrypted passwords had been stolen from about 38 million of its active account holders last year.
And Flash vulnerability alerts frequently appear on security firms'warning lists.
"Adobe does seem to have an unfortunate history of people finding security flaws with Flash that require updates," independent security consultant Alan Woodward told the BBC.
"What Adobe seem to have done in this case is put out a warning, but it has not given as much information as other firms would normally do when issuing such a security advisory.
"That might be them trying to avoid giving the hackers too much information whilst still telling people there is a problem."
Adobe only describes the flaw as being an "integer underflow vulnerability" in its report.
