I ran a full avast scan and the launcher.exe file was the only file detected and so I quarantined it in virus chest.
I ran a full MBAM scan and NO files were detected as malware.
If you ran the Avast scan first, then MBAM may have had nothing to pick up as a threat. We do recommend that any threats/infections in the Virus Chest (VC) remain there for 1.5 - 2 weeks. You can, however right click on the item(s) in the VC to rescan it, especially since Avast just put out a large update. If the rescans still comes out as infected, then it is malware and leave it in the VC. Should it come out clean, you can restore it.
I also would appreciate it if someone could answer these questions that I have:
1) Are there ways in which the launcher.exe could have been clean when I downloaded but later infected by something else? (Note: this is the one and only infected file picked up by the avast scan on the whole computer. And also that I downloaded the file from a source that I believe to be trusted - the official game website)
2) Is it unusual that SuddenAttackSEA was under the exclusions for the File System Shield when I don't remember ever putting it there myself?
1. Not unless it is a FP, in which case follow the directions I posted above in THIS post for rescanning items in the VC after Avast does periodic updates.
2. Yes, very unusual. Does anyone else use your machine? Did you check for a keylogger or other type of malware that allow remote access to your machine?
Other suggestions I have for you are:
Keep your definitions up to date for both Avast and MBAM. Keep all your shields on with Avast, do Quick scans with MBAM, and add things to your browsers for safer browsing.
You may also want to check to see that your software is up to date with the free Secunia Software Inspector
http://secunia.com/vulnerability_scanning/personal/ since software is changing all the time. This site gives you the vendor's direct download link making it easy to upgrade your software. Many of us here scan our machines weekly.