We seem to have a security issue here in the Oauth implementation of Widar. I'm able to edit under some else his/her account see https://www.wikidata.org/w/index.php?title=Q22135494&type=revision&diff=293822691&oldid=293822124 for an example. I didn't do anything to compromise this other account, it just happened.
This should be handled as a security incident.