PC and Mac users are being advised to ensure that their computers are updated with the latest security patches, following the discovery that the notorious Angler exploit kit is taking advantage of a known vulnerability in Microsoft’s Silverlight technology.

Silverlight, Microsoft’s attempt to rival Adobe Flash, is an application and browser plugin that allows PC and Mac users to watch online media content.

According to security blogger Kafeine, a recently updated version of the Angler exploit kit has been spotted taking advantage of a critical remote code execution Silverlight vulnerability that Microsoft patched in January.

At the time, Microsoft explained that the vulnerability (known as CVE-2016-0034) could allow hackers to infect vulnerable PCs and Macs without requiring any user interaction. All that would be required would be for a victim to visit a website harbouring a boobytrapped Silverlight application:

The vulnerability could allow remote code execution if a user visits a compromised website that contains a specially crafted Silverlight application. An attacker would have no way to force users to visit a compromised website. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email or instant message that takes users to the attacker’s website. If a user is logged on with administrative user rights, an attacker could take complete control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

The Silverlight exploit was uncovered by researchers at Kaspersky following an examination of information which leaked onto the net following the security breach at the controversial Italian spyware firm Hacking Team.

When Hacking Team was itself hacked in the middle of 2015, putting its shady list of government and intelligence agency clients at risk, a number of new zero-day vulnerabilities used by the firm were made public, forcing the likes of Oracle and Adobe to update their Java and Flash software with security patches.

Once again, online attackers have proven themselves eager to evolve their malicious code and willing to exploit newly discovered vulnerabilities in their attempts to infect as many computers as possible.

Every time you add a third-party technology to your computer you are potentially increasing the size of the attack surface that an attacker can target. If you really must run Microsoft Silverlight, please make sure that you are keeping it up-to-date. If you have disabled its auto-update feature, reconsider whether that was a wise decision.

Remember – you don’t have to be running a Windows PC to be vulnerable to a security hole in Microsoft’s software.