Why "spam %"

[MercuryHero]

I've read a bunch of articles about the change from "Impression CTR" to "Impression spam %" and so on, and while I get that this is just a change to the way it's reported and it's nothing to worry about, none of these articles seem to have actually explained why it's called that and why Google needed to change the term at all. Why "spam %"? It just seems really strange and I don't get how it's another way of saying CTR.

[MayankParmar]

It's a bug. But I dunno how the engineers come up with such bugs :P

[NickMNS]

And how they let it persist?

[Travis]

They may have a "spam" metrics used internally, and the label being accidentally popping. Because, it's obvious that Adsense has much more metrics than those they are letting us see.

[MercuryHero]

Could it really be a bug?... It's been like this long enough for articles to have been written about it that are findable on Google. I'm not sure I buy this - Adsense is a pretty big thing to Google and I wouldn't have thought they'd mess up something like that much less leave it like that for so long if there wasn't some thinking behind it...