Even though a comment on your Instagram might look like junk, it could actually be a Russian malware.
They comment how to get in touch with its controllers and recently they had a comment on a Britney Spears photo.
The malware was situated in a Firefox browser extension pretending to be a security feature and it would search for hidden links in order to connect back to its control server.
The comment has been deleted but it had a web address that required a fairly complicated, multi-step process to decipher.