Password protection

I have a spreadsheet that is shared by many users.
I maintain the spreadsheet and the others have read only access.
When I opened the spreadsheet this morning it opened without asking for my password.
This has me very worried that someone may be able to change things within the spreadsheet.

Why would the spreadsheet stop asking for my password?
How can I check the security settings?

Thanks

Excel is not a very secure environment, and passwords can easily be broken. To check the settings click on the Review tab and then Protect sheet (or Unprotect sheet if a password applies).

Hope this helps.

Pete

Thanks for helping.