It took just a day for cybercriminals to start using a new and yet-to-be-patched Flash Player exploit that was leaked from a surveillance software developer.

The exploit was found by security researchers yesterday among the 400GB worth of files stolen recently from Hacking Team, an Italian company that develops and sells intrusion and surveillance software to government agencies.

Adobe Systems confirmed the vulnerability, which received the identifier CVE-2015-5119, and is planning to release a patch for it later today. However, cybercriminals have already jumped on the opportunity to use it to infect computers with malware on a large scale.

According to a researcher known online as Kafeine, the leaked Hacking Team exploit has already been integrated into three commercial exploit kits: Angler, Neutrino and Nuclear Pack.

Exploit kits are Web-based attack tools that leverage vulnerabilities in browser plug-ins like Flash Player, Adobe Reader, Java or Silverlight to install malware on computers. These attacks are typically launched from compromised websites or through malicious advertisements.

“This is one of the fastest documented cases of an immediate weaponization in the wild, possibly thanks to the detailed instructions left by Hacking Team,” researchers from security firm Malwarebytes said in a blog post.

The Hacking Team exploit was leaked together with a detailed readme file that contained instructions on how it works and how to use it.

Until the Adobe update is released and installed, users are advised to enable the click-to-play feature in browsers that support it, like Google Chrome and Mozilla Firefox, or to disable the Flash Player plug-in in their browser.