If by stable you mean it's as secure as a screen door on a submarine then, yes, it's "stable" ...
https://www.theguardian.com/technology/2017/nov/08/cryptocurrency-300m-dollars-stolen-bug-ether
http://fortune.com/2017/08/28/ethereum-cryptocurrency-stolen-bitcoin/
https://www.coindesk.com/30-million-ether-reported-stolen-parity-wallet-breach/
https://medium.freecodecamp.org/a-hacker-stole-31m-of-ether-how-it-happened-and-what-it-means-for-ethereum-9e5dc29e33ce
https://www.cnbc.com/2017/07/20/32-million-worth-of-digital-currency-ether-stolen-by-hackers.html
https://www.theverge.com/2016/6/17/11965192/ethereum-theft-dao-cryptocurrency-million-stolen-bitcoin