I was googling randomly and then I entered 999999..999999 which led to the linked page. Though not a crash, but since it said that it detected a huge traffic from my computer which was not the case, I used the term crash. It did mention, though as the last explanation point, that it might have been caused by a term that is actually used by robots, it still didn't clarify what kind of robots was it talking about.
Was the reference to the crawlers and bots, or did it mean something different entirely?
It's because this is a range search, as denoted by the "..". See here for discussion: http://news.ycombinator.com/item?id=2948873
I don't think there was any definitive answer but a number of hypotheses, in particular this one seems reasonable:
The reason for this is that you can google ranges of numbers, and people a couple of years ago were using this feature to find credit card numbers that were posted online, eg searching for 4000000000000000..4999999999999999
Whether for cc numbers or something else, it's likely a defence against dubious searches: the error message indicates that the search violates Google's ToS.