I have seen many words related to 51% attack but I never knew which coin does really suffer it.

If someone really starts 51% attack, he/she will need huge hashpower and is hard to make profit?

So, is anyone know which coin ever suffers 51% attack?

For now, there are so many coins having very low hashrate. They are really in danger?

For example, infinitecoin (IFC) is an old coin and only has less 10Mh/s net hashrate (one L3 has 504Mh/s).