Not sure, how many of you are aware of this alert. Oracle has published an Alert document NOTE:726418.1 -ALERT: The 10.2.0.4 Windows Patchset Overwrites %ORACLE_HOME%\network\admin\sqlnet.ora
According to it, Patch 6810189 - 10.2.0.4 RDBMS patchset on Microsoft Windows (32-bit) and Microsoft Windows (AMD64 and EM64T) overwrites the %ORACLE_HOME%\network\admin\sqlnet.ora file.
In case you have Downloaded (and installed) the 10.2.0.4 patchset for Windows before 10 July, 2008 , then please download the software again. In case you have not customized the sqlnet.ora file, then no action is needed.