Situation was complicated but he clearly made some bad decisions . They way I understand it is that he met someone through an online course A noncredit MOOC and talked the girl into sending and participating in exchange of explicit material and explicit conversations . The girl participated for about a year controversial because it could have been mutual given it was all online and the girl could have cut ties at any point instead of participating for a year but the girl was also vulnerable and suffered from depression , anxiety , and selfharm . University found out , investigated chat logs and pictures , and cut all ties with him though no criminal charges came out of it . TLDR Professor did something unethical , but not strictly illegal . MIT cut ties with him based on evidence of harassment and unprofessional behavior .