According to CNET, Yahoo Answers was flooded with threads on the topic, and users who were locked out were shown the following message, which led to them being required to upload photos of government-issued identification by Feb. 1:
Your account has been secured and requires account validation. Please login to Instagram.com from your desktop computer to validate your identify.
A Facebook spokesperson told CNET:
Instagram occasionally removes accounts due to violation of terms and, depending on the violation, may ask people to upload IDs for verification purposes.
Readers: Were any of you blocked from accessing Instagram?
Screen grab courtesy of CNET.