The attackers are trying to trick users into clicking a link which directs to a website serving malicious Flash (SWF) content and, according to the security bulletin released by Adobe, Firefox users are particularly at risk.
The update fixes three vulnerabilities in total (CVE-2013-0504, CVE-2013-0643 and CVE-2013-0648), but currently only the latter two - a Flash Player Firefox sandbox flaw and a vulnerability in the ExternalInterface ActionScript feature - have been spotted being exploited in active attacks.
Users who have set up automatic updating for Flash need only to wait for the updates to be pushed out. The rest are advised to download patched version for Windows, Mac and Linux.
Windows and Mac users and administrators are urged to do so as soon as possible, while those using Linux can do so at their discretion.