I can not understand why you can not give him a second chance? If suddenly the situation recurs (although I am sure that this will not happen anymore) you will block for ever After all, 1 post was published. As stated above, the password will be changed, and it will be more responsible in the future. Yes, I know English badly, because I translate you with the help of a translator.
Have a look through the last few pages of the Meta board. You will find several posts on each page from people complaining they were banned following an instance of plagiarism. None of them were given a second chance. Why should you be any different? Your excuse that a hacker broke in to your account, made a single post and then never returned is obviously false.
Rules are rules. If you break them, there are consequences.
How then can we explain the fact that he did not leave this message, but it was on the forum? He says he never even went into this thread to which you indicated the link above. As for me it is not fair to ban for what the person did not do, he is sure that he would be ready to go through the detector, because he needs this account for work, but now as you can see it stops ... I am sure there should be ways for which one can prove the owners innocence, because we are now discussing account blocking not on the women's issues forum, but on the forum where a person earns, and how stupid it is to understand how to deny a person access to work