>>How should I interpret that?
>
>Isn't sa the default account for SQL Server? Is it password protected? Is someone trying to use it to access your server?

It looks like it. Yes, sa is the default SQL Server account. I know it should always be password protected, but I'm not sure how strong our password is.

Is there a quick way to check what autentication is used in SQL Server?

Let me find out.

BTW, which Event Viewer did you check that time? Did you find similar entries?

Thanks again.