Summary:
The users of Web TimeSheet are able to see even projects that they are not part of in the Projects drop-down list on their timesheets. This allows them to enter time against those projects.

Resolution:
If a project team has All assigned to it, all the users will be able to enter time against the project. To resolve the issue, ensure that you only add a department or an individual user to the project team and remove All assignment from the project.