What is the Guest account in SQL Server 2K,2k5 and above?Database Users > guest User
What is the use of this account? Do we really need this account?
You can think of it as the default anonymous User, or "Everyone".
When does sql uses this account ?
When a person logged into to an Instance tries to connect to a database and their Server Login does not have a Database User mapped to the database then SQL Server will attempt to connect them to the database using the guest User. If the guest User is disabled then they are denied the ability to connect to the database.
What if we disable account ? What will if i disable it ?
You can disable it in your User-databases, and you should if you have no need to allow anonymous access into that database, but do not mess with it inside the System databases, e.g. msdb.
__________________________________________________________________________________________________There are no special teachers of virtue, because virtue is taught by the whole community. --Plato