Hi TonyG
Interstellar stores your private keys encrypted with your password on your browser's localstorage. We do not store or use your secret keys anywhere else.
What device did you use to create your account?
Did you create a new account on Interstellar, or did you import secret keys from somewhere else?
Did you store your secret keys anywhere else?
Did you import multiple accounts ? (Maybe you are seeing notifications for transactions from another account).
If you fear your account has been compromised, I suggest you transfer your funds to a new stellar account.
Maybe your device itself is compromised. There are two ways to secure your next new account. You can either use a hardware wallet, or use multisig (we recommend 2 of 3 multisig accounts. 1 key on your PC, the other key on your smartphone, and a third key stored on paper in a safe location. Feel free to store your keys anywhere else you think is safe). Interstellar supports multisig accounts.
Finally, there are stellar explorers you can use to track activity using only the public key. (https://stellarchain.io and https://steexp.com). You can also post your public key here on this forum. I, or someone else might help you track where your lumens went to.
