A recently patched Flash Player exploit is being used in widespread attacks

The vulnerability, known as CVE-2016-4117, was discovered earlier this month by security researchers FireEye. It was exploited in targeted attacks through malicious Flash content embedded in Microsoft Office documents.

When the targeted exploit was discovered, the vulnerability was unpatched, which prompted a security alert from Adobe Systems and a patch two days later.

As it usually happens with zero-day exploits, it was only a matter of time until more cybercriminals got their hands on the CVE-2016-4117 exploit code and started using it in widespread attacks.

On Saturday, a malware researcher known as Kafeine spotted the exploit in Magnitude, one of the most popular exploit kits used by cybercriminals.

Exploit kits are Web-based attack tools that bundle multiple exploits for vulnerabilities in browser plug-ins like Flash Player, Java, Silverlight and Adobe Reader. They are used to silently install malware on users' computers when they visit malicious or compromised websites.

Another way to direct users to exploit kits is through malicious ads posted on legitimate websites, a technique known as malvertising.

Unlike cyberespionage groups, exploit kit creators and operators don't mind if their exploits are for patched vulnerabilities, because they count on the fact that a large number of users don't frequently update their software.

However, the fact that it took them less than two weeks to find the exploit and add it to their tools, increases the number potential victims with a vulnerable Flash Player installations.

In order to stay protected users should make sure that they're running the latest version of Flash Player available for their browser and should also make sure that the other browser plug-ins are also up to date.