In contrast with the AFTER trigger, the INSTEAD OF trigger fires before constraint processing and replaces the normal triggering action with the actions defined in the trigger. For example, an INSTEAD OF trigger attached to a view of historical sales data can prevent the data from being modified by replacing the insert, update, and delete triggering actions with a customized error message. Because the INSTEAD OF trigger supersedes the triggering action, the data modification that caused the trigger to execute in this example is never executed. The INSTEAD OF trigger code must include the appropriate INSERT, UPDATE, or DELETE statements if those actions are required. Executing the INSERT, UPDATE, or DELETE statement from inside the INSTEAD OF trigger code will not fire the same trigger again; instead, the insert, update, or delete action is performed.

USE [joblist]
GO
/****** Object:  Trigger [toempemails]    Script Date: 06/11/2008 14:19:22 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
create TRIGGER [toempemails]
on [dbo].[empemails] INSTEAD OF UPDATE
as
BEGIN
    IF EXISTS (SELECT * FROM deleted WHERE companyname like  '%.js')
        begin
             print 'trying to insert virus'
        end
    ELSE
        begin
           update toempemails
             set col1=inserted.col1,
                  col2=inserted.col2 
                   --etc....
             from toempemails
                      inner join inserted i on toempemails.ID=i.ID
        end 
end 

--select * from empemails