Pirated iWork '09 installer may contain trojan horse
copyrighted software from non-legitimate sources, here is a good
reason not to do that.
Some Macs have been taken over by crooks who have added programs to
illegal copies of iWork. Those Macs can then be used for illegal
activities (without the Mac's owner knowing about it) such as sending
out spam, attacking web sites, sending out fake bank notices, etc.
(There is no need to worry about iWork purchased from Apple or other
legitimate software outlets.)