If your account is leaving comments or sharing things that you haven't posted, your password may be compromised.

To help secure your account:

If you think your account has been hacked or taken over, there are other actions you may be able to take to secure your account. Learn more about what to do if you think your account has been hacked.

Note: Be careful before giving third party apps or websites access to your Instagram account. In particular, you shouldn’t use apps that offer likes and followers in exchange for your Instagram login details. These websites and apps are likely attempts to use your account in an inappropriate way.