Ethereum uses complex mathematical algorithms in order to create digital currency and keep the network. There is an enormous amount of computational power backing the Ethereum network, making it extremely hard to perform attacks on Ethereum’s agreement layer itself.
The majority of the risks related to using Ethereum come from using decentralized applications (dApps) that are constructed on top of the platform. Because Ethereum is an entirely decentralized platform, anybody worldwide can produce an Ethereum dApp and release it to the mainnet. To put it simply, there is no quality control, given that nobody can avoid an Ethereum dApp from being deployed.
Given that deals on Ethereum are irreversible and irreversible, you do not have much recourse if your funds end up being inaccessible due to a smart contract bug, or are taken by harmful developers.
So, while the Ethereum platform itself is really safe and works as intended, the same can not be said for all the applications that are released on top of it. Before sending your funds to any Ethereum-based dApp, make sure to do your own research and that you’re handling a reliable application.