Did I have malware? Do I have to change passwords?

After installing this update I have no idea if my security was ever compromised by Flashback malware. If it was, I want to change my passwords. If not, I don't want to change them.

If there's a serious threat shouldn't updates tell us if we were affected? It seems like it just erases the malware and closes the security vulnerability, which is great going forward. But if they've already got my data, doesn't the update just erased my history of exposure to the malware? That actually leaves me more vulnerable.