As long as the files inside of each addon folder only contain txt, lua, toc, xml, and graphic files then you should have no reason to worry. Curse and WoWInterface are the only two places that I will download from, aside from the one or two beta addons I try from the WoWAce site, and I haven't heard anything about Atlas Loot from Curse containing any keyloggers.
When someone is hacked, that doesn't mean that they just recently became infected. It's well known that those keyloggers sit on your computer for quite some time before the hackers even try to gain access to your account, and it's not just the WoW account that gets compromised. Anything that you use a login and/or password for is also compromised. Your email account(s) (especially the freebie web ones), forum accounts, banking, and any other type of account that you use a login or password for.
Try better prevention to stop it before it can be downloaded. Use a free custom host file and the free service called OpenDNS (public schools and public libraries use this service). Block it before it ever has a chance to even show up in your browser.
Use Hostman to apply a custom host file to your computer.
http://www.abelhadigital.com/2008/07...-released.html
Use OpenDNS to block the ability to get to sites that are known to have harmful flyby downloads.
http://www.opendns.com/
As for the things you manually download to your computer, do like the admins here do with addons that people upload. Open each addon you download and look at the files inside. Manually check everything, then scan it, then scan it again.
Edit: The Authenticator is also another layer of protection for you (looks like they're in stock.. I would grab one before they sell out again!).
http://us.blizzard.com/store/details.xml?id=1100000622