A number of Instagram users have taken to social media to report a mysterious hack in which their profile photos are replaced by random stills from films.
Their account names have also been changed and they are unable to log in.
Their registered email addresses have also been been altered to accounts originating from the Russian email provider mail.ru.
Instagram said it tries to provide a safe and secure experience for its community.
“When we become aware of an account that has been compromised, we shut off access to the account and the people who’ve been affected are put through a remediation process so they can reset their password and take other necessary steps to secure their accounts,” said a spokeswoman.
Instagram has security tips and advice about hacked accounts on its website.
It has also published a blog saying it continues to investigate the issue.
The hackers have so far made no demands and the affected accounts appear otherwise untouched.
There are tweets describing the hack dating back to July.