New feature was introduced in Oracle 11g. It is called as Authentication attempts restriction.
If any hacker is able to start server process without using any username and password then intruder is also able to execute loop for gussing password for user account. He or she can start to ping database using different password guessing and may be get success. For priventing such kind of attack of hacker, you can enable authentication attempts restriction parameter at database level.
New article has been published with full detail of this new security feature of Oracle 11g in our Oracle DBA tips section.
It is very useful feature for every remote dba support services. Because using this parameter you can restrict such kind of hacker attack without affecting valid user connections.
Wish you all the best,
Remote DBA services team