[TYPO3] Need explanation on Administration log

[Bing Du]

Hi,

Typo3 V4.0.2

Are there any documents on explaining what each part in the administration
log means?  In Tools->Log, most entries are like

Time  User      Type  E  Action  Details
15:52 foo at LIVE LOGIN    LOGOUT  User foo logged out from TYPO3 Backend
(msg#255.2.1)

What does msg#255.2.1 mean?  Is more detailed information stored somewhere
else?  Almost all the entries are just logout information.  Where are
logins logged?

I also I just see my account (with admin access) has some 'logged in from'
log entries like:

Time          User   Type   E Action  Details
08:31 me at -99                  LOGIN   User me logged in from 1.2.3.4()
(msg#255.1.1)

What does '-99' mean?  I also want to know what other connections were
coming from.

Anyway, I'd appreciate explanations or pointers regarding the log.

Thanks in advance,

Bing