Select LogIP, Count(*) as aantal
From
(
    SELECT [LogIP], Count(log_id) as aantalLogins
    FROM [e-Boekhouden.nl].[dbo].[tblLogins]
    where [LogDatum] >= DateAdd(day, -180, getdate())
    group by [LogIP], DATEDIFF(day,LogDatum,getdate()) / 30
) sa
group by sa.LogIP
having Count(*) > 1