Why its shoing -257 in my rating graph?

Describe your bug

I am seeing 974(-257) in my profile though my rating is same as last week i.e 1352
Codechef is going to decrease my ratin? if yes then why?
Its also showing Plagiarised in START88D
what is this? i have not done anything wrong.


Additional info

Check your email. Maybe in Spam as well. You would have received details about the plagiarism.