It turns out that 80% of the Bitcoin miners are concentrated in the hands of very few people.
A lot of people are connected to the few pools. Maybe around hundred thousand individual miners. Should the 51% attack really happen, it would hit all the Bitcoin news and discussion places, and the individual miners would choose different pool. I dont worry this to happen though, its sure way to ruin the pool reputation and steady income.
Wouldn't that be too late? Also how many of us actually check the IP address of the pool mining server. Dont most of us use DNS name? If they point to same IP, how many days will pass before anyone realising that one group has majority stake.
It doesnt matter if someone has majority stake like the top two pools if they are really tightly affilated, but if they actually do the 51% attack to reverse the transaction. It would be actually detected quite fast, as they would probably need to orphan at least 3 blocks (most services need more than one confirmation for larger sums), and even with 75% hashrate this race who get longest chain against remaining 25% with already 3+ blocks could take hour or more.
Too late? You cant never prevent it anyway, the 51% attack can come suddenly out of nowhere as well.