Alert: Javascript dialog box

Have you encounter this type of alert?

I was surfing through some site and this popup suddenly caught my attention. I read the content of it, and i clicked on the "x" button on top right. Be alert of this type of popup as it may install vulnerable software onto your pc after you agree to it. After clicking the "x" button, another windows popup.

This time, it's the permission request to ask for your agreement to install the software on your pc. I'm lucky it was only a error scanning program that will scans my pc. But luck isn't always there...

Beware!