Sorry about the confusion, but I was looking at the wrong account. I checked the FTP logs, and even the backups and was not able to locate any information regarding the default.htm file you are referring to. The logs only go back so far, and it may have been too many days since it was uploaded to check the logs still.
We put a default.htm file on new accounts or accounts that do not renew, but it is blue, instead of black and white. If this occurs again, I would recommend contacting Live Tech Support
while the file is there, or right after you notice, so we can investigate further.
If you suspect something was compromised, I recommend rotating your AMP
If you have any further questions, feel free to post them below.