If you’re a Windows user of any stripe, there’s a recent Patch Tuesday update that cannot be ignored. Microsoft has fixed a vulnerability that was exploited in the wild to serve up malware, mostly in South Korea. The relevant update also contains fixes for several other remote code execution vulnerabilities.

Symantec posted that although the Internet Explorer Scripting Engine Remote Memory Corruption Vulnerability was patched, it had been seen in the wild before then. Assigned CVE-2016-0189, it “allows attackers to surreptitiously execute malicious code when vulnerable computers visit booby-trapped websites,” Ars Technica reported.

How the Exploit Worked

According to Symantec, once the victim landed on the malware’s page — perhaps sent there by a phishing email — JavaScript in the page code profiled the computer. It checked to see if the computer was a virtual machine and determined which version of Internet Explorer, Flash and Windows it was running.

After that, the JavaScript would activate the exploit, which would download a malicious file and save it to the computer for execution.

The origins of this attack can be traced back to 1999, when South Korea required online vendors to adopt Microsoft ActiveX. BetaNews reported that, at the time, the government wanted all online transactions to use the SEED cipher developed by the Korea Information Security Agency (KISA).

It has since reconsidered this action, which made the country heavily dependent on Microsoft Internet Explorer for routine use. This dependency also makes organizations easy targets for exploits that play on IE — such as this memory corruption vulnerability.

More Vulnerabilities for Patch Tuesday

Adobe has also warned about a zero-day exploit for Flash Player that it found in the wild. According to the alert, it could cause a crash and potentially allow an attacker to take control of the affected system. This vulnerability affects all major systems that run Flash Player, not just Windows.

Adobe said it will patch Flash today, May 12. While this may not be a Tuesday, it is still essential for users to patch problems quickly and stay on top of relevant alerts.