Hi,
Nobody tried to hack your account, the plugin does not have functionality to save or send your data to a different resource – the data are only sent to google. Sometimes the authentication error occurs, that google considers as an unautorized login attempt.
In case you failed to add a sitemap to Google automatically using Google Sitemap plugin (by Bestwebsoft) and you received a message notifying that your login and password do not match, it is possible to do it manually.
Instruction: https://docs.google.com/document/d/1VOJx_OaasVskCqi9fsAbUmxfsckoagPU5Py97yjha9w/edit
Sincerely,
BestWebSoft Support Team