Each Monero wallet gets a unique word-sequence called a mnemonic.
It's the only way to regain access, and it's never sent to the server!
If you save it to an insecure location, copy, screenshot, or email it, it may be viewable by other apps.
For large amounts and better privacy, make a cold-storage wallet or set your own server in Preferences.
The convenience of MyMonero for web comes at a security cost.