de0u In theory blockchains are subject to consensus hijacking by powerful parties, and in practice sometimes it happens. Here is a claim about Monero: Monero faces 51% attack. I guess if you have an XMR mining setup that is currently turned off, this might be a time to turn it on.
Probably9857 de0u And if you're receiving Monero, maybe wait for more than 6 confirmations before considering it really received. (I believe Monero block times are about 2 minutes, so that's still not too long compared to other chains.)