It isn't necessarily on the homepage. I remember reading about that service they provide, though I must admit it was ages ago.
From what little I remember, it basically works like this:
When there is malware on something anyone clicks, or as a pop-up, some browsers report that. Usually we, the users, give permission for such reports to be sent, when we agree to it. We may agree to it simply by agreeing to use the browser, or by not deselecting the option within settings. It will probably work differently, for different browsers.
Those reports are sent to "the powers that be" for that browser. Then a program checks to see what site they were on, and what they were doing. "What they were doing" refers to either clicking, or watching a vid, or nothing at all, etc.
When enough of those reports are received, either a specific limit is reached, or an amount within a rolling window of time, then users of the browser will be alerted about it, whenever they try to access the site, or page that has been registering the red flags.
I'm sure it is a lot more technical than that, but that's the jist of if.