If it's from the official Sims website (for Sims 3) then there's not really any chance of getting viruses.
If it's from random Sims items sites, there's a possibility, especially if the site looks unreliable. But I'm not entirely sure downloading items for the Sims was the only cause of you get viruses. Perhaps something else did it too.
And no, I'm no expert. This just sort of made sense to me.