Oracle table access

Hi,

I have my Oracle on Unix boxes. There is one database - abcdw There is one schema sch1 and there si one userid and password to see that schema.
Now 2 people are using toad on windows. One person is able to see data in that schema while the other can't They are both differentiated on windows andunix by a userid - but that should not matter to Oracle as far as I know. Also I see that they have in their log something like
user1 logged in
user2 logged in
How are they finding the userids [which are not related to Oracle but Unix ldap]?

Thanks