Internet Explorer is pre-installed on every Windows PC, even though it’s been superseded by Microsoft’s new Edge browser in terms of long-term support.

The reason is simple: Many organizations use the archaic browser for legacy applications, and so Microsoft has had to keep it around but isn’t spending a great deal of time on improving it.

Unfortunately, according to one security firm, Internet Explorer has a serious flaw that’s leaving it open to malware attacks.

ZDNet reports on the zero-day bug, which is coming from Chinese antivirus software company Qihoo 360 Core.

The company’s security research team claim that the bug uses a Microsoft Office document that has a vulnerability installed that opens a web page that downloads a piece of malware.

According to the researchers, the malware exploits a user account control (UAC) bypass attack, and it also utilizes file steganography, which is the technology of embedding a message, image, or file within another message, image, or file.

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