#1 - Aug. 6, 2010, 11:13 a.m.
No one can ever guarantee a scan has found everything.
All you can do is make sure your scanners are up to date, use them appropriately and be vigilant. Even the best scanners won't be good for a brand new threat until they are updated.
What you can do is add an authenticator to your account as an extra layer of security, scan regularly and be vigilant against scam attempts through tells and emails.
As to a timeframe, that can vary quite a bit. At the moment, restorations are only running a few days.
This sticky may be useful.
Account Hacked? Security Issue? Look Here!
http://forums.worldofwarcraft.com/thread.html?topicId=24702231244 You may also want to look into getting an authenticator for your account. It's no substitute for good security habits, but it will help keep them out of your WoW account.
Blizzard Store
http://us.blizzard.com/store/browse.xml?f=c:6 Mobile Authenticator
http://us.blizzard.com/support/article.xml?locale=en_US&articleId=26109