Warning: ethexploit.org is a scam

The authors of the website claim to have found a bug in Ethereum smart contracts that lets you double your eth via a vulnerability that "requires ten pages of documentation for a detailed explanation", and ask you to send eth to a smart contract address they provide to prove it by doubling your eth. Of course, it will just steal your eth.

Whois shows the domain was registered Feb 10th so pretty new.