Reports and logs
Two backend modules in TYPO3 require special attention: Reports and Log:
The Reports module groups several system reports and gives you a quick overview about important system statuses and site parameters. From a security perspective, the section Security should be checked regularly: it provides information about the administrator user account, encryption key, file deny pattern, Install Tool and more.
The second important module is the Logs module, which lists system log entries. The logging of some events depends on the specific configuration but in general every backend user login/logout, failed login attempts, etc. appear here. It is recommended to check for security-related entries (column Errors).
The information shown in these (and other) modules are senseless of course, in cases where a compromised system was manipulated in the way that incorrect details pretend the system status is OK.