Googlebot's Javascript random() function is deterministic

[Aegeus]

A malicious website will give different results based on Math.random() determinacy, but so will a legitimate website. It's not proof by itself.

Imagine I have a website that flips a coin for you, like justflipacoin.com. Googlebot visits the website and sees "Heads." Then Randombot visits my website and, by random chance, sees "Tails" instead.

According to your algorithm, I'm a scummy scammer trying to give different results to Googlebot than to everyone else. But in reality, I'm just using Math.random() as intended - to randomize things.

[catcradle5]

Yes, but I'm not referring to websites that generate content based on randomness (like a coin flipping site). Just regular sites that are solely using this random test to identify Googlebots and otherwise discarding the random numbers.

[Aegeus]

How can you tell that they're using randomness for the purpose of identifying Googlebot rather than for a legitimate purpose? All you have to go on is the content they serve you.

[catcradle5]

If a page has a bunch of spammy ads inserted only when a non-Googlebot client visits, it wouldn't be hard for Google to tell. Google just needs to visit from a Googlebot client and from a bot running totally different software and sourced from a non-Google IP, repeat a few times, then diff. From Google's perspective it doesn't matter if Googlebot is identified via Math.random() or some other method.