Adding a buff to a unit

is there a way to add a buff to a unit through triggers? or do u have to add an ability. and if you DO have to add an ability, how can u have the ability not be shown in the units control panel?

replies are greatly appreciated

1. u use an ability that has a buff, modify its propertis so it does nothing and cast it on the unit.
2. place an aura into a spellbook and use my function.

For the no-icon aura, couldn't you use Tornado's slow aura, I think that one doesn't display an icon...