Mashable says a small number of users have noticed unusual activity with their account. They're unable to log in and then are alerted their account doesn't exist. A hacker is gaining access and changing information, like username, phone number and email address linked to the account. The hacker is also changing profile pictures to Disney characters.
Instagram has addressed the issue on Twitter (see below), but users are concerned the issue will become more widespread.
We are aware that some people are having difficulty accessing their Instagram accounts. If you think you have been impacted, please follow our guidance to regain access: https://t.co/DfHpQuk9SJ— Instagram (@instagram) August 15, 2018