Start Session

Here is the process on the site before I ask the question:
User logs in
session is created based on username and userid
user edits a record in the db
a hidden field with the userid session is inserted in the db to show
who edited the record

I had a user ( mike, id -1 ) edit a record today but the userid that
got inserted was 2 ( scott ). mike doenst know scotts credentials and
scott has never used the PC that mike is using, matter of fact scott
hasnt even logged into the site today.