I used w3t_Users and yes, the board prefix is w3t. I ran the query again, as I may have used a lower-case "users" the first time. The report I got was "1 row(s) affected by your query", and at first it didn't seem as if any users were deleted, but after I'd reloaded the main message board page I can see that about 1000 users were removed. So, thanks for your help