WHM does not send out an e-mail upon someone logging-in; the e-mail would have been generated by a non-stock modification or third-party software.
I recommend checking the following two log files and cross-referencing similar entries (e.g., those with a matching IP address) to help determine specific information about the login attempts and what, if anything, was accessed beyond the attempted login:
Code:
/usr/local/cpanel/logs/access_log
/usr/local/cpanel/logs/login_log
If using cPHulk the following log file may also be checked:
Code:
/usr/local/cpanel/logs/cphulkd.log