I've always been a skeptic of my privacy of In Browser Ethereum Wallets Such As MetaMask. I currently have several tokens stored in my MetaMask. This has since changed and I'll explain why according to John Backus.
1.) If you have an In Browser Wallet Any Website Can Detect If You Are An Ethereum (ETH) User. Metamask for instance injects a global web3 object into the page. Below is a snapshot from John Backus @backus Twitter page
Metamask can't send transactions without your knowledge however its very easy for any advertisers or websites to know how much Ethereum you own.
If you use Metamask one of the best tricks I've learned is to only ENABLE Metamask when you are using it ONLY. Afterwards go to "Extensions" and simply DISABLE it.
Hope this has helped you in keeping yourself better secured. The little steps in protecting yourself and digital coins is the most vital.
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