I had a ten year old site virtually de-indexed as a result of someone plagiarising one single page. It wasn't even an attack as such, just someone being too laz

I had a ten year old site virtually de-indexed as a result of someone plagiarising one single page. It wasn't even an attack as such, just someone being too lazy to at least re-word the article. This was within the last 3 years. Until then, I too believed Google were 'smart enough' to recognise such things.