Help, somebody has been making it look like my mother sends pornagraphic messages on Facebook,

My mother logged onto her ফেসবুক account and found that several messages had been sent to her ফেসবুক friends, for example:
oYur naekd danecs wree fimled! (don't প্রতিবেদন me for putting this I'm trying to help my mother salvage her reputation) who অথবা what did this and how can we stop them?