1. If your ledger would be hacked, all funds would be gone already.
2. If the total amount of your coins inside of your wallet still is correct, it indeed is a change address of yours.
Bitcoin transactions work with inputs and outputs.
For example:
You (A) have 1 input (i.e. received 1 transaction) with 1 BTC.
You want to send 0.1 BTC to B.
The transaction looks like this (ignoring fees here):
Input:
Outputs:
- 0.1 BTC (to B)
- 0.9 BTC (to yourself)
Your wallet will show 0.1 BTC being transferred.
On a block explorer however, you will see that your whole BTC has moved (which is true, but 0.9 of them moved to a different address of yours).