have you recently added Google SEO plugin ? if so check at its place on the plugins page - does it provide any instructions ?
and you have wordpress site at the parent folder. its .htaccess might be affecting MyBB
Thanks for the quick message. Seems like .htaccess has been tempered. Replace it with new changes.
No changes has been made from our side. If it is a hack, how to prevent from happening in future.
I do not see hack attempt. the links are working now