user89359: I am new to Bitcoin. I used Electrum software to create my first wallet. When the software generated 12 words, I had written down that in paper. These word are very important, right? But the software can see these words and stores them somewhere in their server. So how do I know that they don't use my wallet because they have my seed? Sorry if it's a dumb question.

user7272: Electrum does not store your seed, the server is run by volunteers, and you can run your own if you wish.
You needn't take my word for it: Both Electrum and electrumx are open source, and you can verify the functionality, and build a version from code you have verified.

89359: <p>I am new to Bitcoin. I used Electrum software to create my first wallet. When the software generated 12 words, I had written down that in paper. These word are very important, right? But the software can see these words and stores them somewhere in their server. So how do I know that they don't use my wallet because they have my seed? Sorry if it's a dumb question.</p>
 7272: <p>Electrum does not store your seed, the server is run by volunteers, and you can run your own if you wish.</p>

<p>You needn't take my word for it: Both <a href="https://github.com/spesmilo/electrum" rel="nofollow noreferrer">Electrum</a> and <a href="https://github.com/kyuupichan/electrumx" rel="nofollow noreferrer">electrumx</a> are open source, and you can verify the functionality, and build a version from code you have verified.</p>
