Quote from: BlackHatCoiner on Today at 12:17:30 PM

Has it ever be insecure to wait between 2 and 6 blocks?

Bitcoin has had two significant reorgs of greater than 6 blocks in the past.

The value overflow incident in 2010 was the result of a bug which created 184 billion bitcoin. Satoshi patched it in around 5 hours, everyone moved to the new patched client, and 53 blocks were ultimately made stale.

The release of v0.8 in 2013 also caused a fork due to a block being mined which was incompatible with v0.7. It was ultimately resolved by users downgrading back to v0.7,'and resulted in 24 blocks being made stale.

Outside of these bugs, the longest reorg I am aware of is 4 blocks, starting at block 174,161.

Quote from: BlackHatCoiner on Today at 12:17:30 PM

I've seen some cases of people who lost money, because two blocks were propagated and the block they had their transaction included got removed. Although, I have never heard it for 2 confirmations.

Even with reorgs of several blocks, it is unlikely for anybody to lose money. Usually the competing blocks include many of the same transactions, and any which are not included in the winning chain just end up back in the mempool to be mined later.