According to the German Federal Bureau for Information Security (BSI), Yahoo has not been cooperating in researching the cyber attacks carried out between 2013 and 2016. This was reported by Reuters

Information of more than a billion Yahoo users was acquired through the attacks. The Yahoo office in Ireland has rejected to share information according to BSI. Yahoo sent the researchers to the Irish Data Protection Commission, however Yahoo did not give permission to the commission to share information.

A spokesperson from BSI has shared that they will bring out information on this matter, because Yahoo has not responded to the research so far. BSI awaits response from Yahoo and the Irish Data Protection Commission