Increment a entry in an sql table via asp.net by 1

I have a database containing usernames and "points". I need to increment the "points" at will. I have the table connected to a sqldatasource.

Here is my current code:

    With Users
        .UpdateCommand = "UPDATE Users SET points = points + 1"
        .Update()
    End With

This works great, except, instead of just changing the entry with the username specified by a QueryString, it changes all of the entries and adds one.

The sqldatasource has the following select command:

SelectCommand="SELECT * FROM [Users] WHERE ([username] = @username)"

This command makes it so that only entries with the querystring specified username are displayed. This is really my first attempt at SQL. Any ideas or solutions would be appreciated.

--EDIT--

Thanks for the help Oded, here is my final solution that worked :)

With Users
     .UpdateParameters.Add(New Parameter("username", System.Data.DbType.String, My.Request.QueryString("username")))
     .UpdateCommand = "UPDATE Users SET points = points + 1 WHERE ([username] = @username)"
     .Update()
End With

You need to specify that only that user row should be updated:

.UpdateCommand = "UPDATE Users SET points = points + 1 WHERE ([username] = @username)"

When a WHERE clause is not specified, the UPDATE will apply to all existing rows, as you have seen.

Edit:

This is an example of how to add a username parameter:

.UpdateCommand.Parameters.Add("@username", SqlDbType.NVarChar, 40, "The User Name");

Add a where clause to your UpdateCommand:

 UpdateCommand = "UPDATE Users SET points = points + 1 WHERE ([username] = @username)"