I don't have the c:\programdata\avast software\avast\spamconf folder on either my XP or win7 systems and both are running avast free. So either it isn't an element in XP or win7 installations, which I doubt, but more possibly it is an element in avast paid versions.
Taking a bit of a guess based on its folder and file name it is an anti-spam feature (and a look at program features at avast.com), are you using an avast paid version that has anti-spam AIS/Premier ?
If so then you should be able to open its settings and looking for any log/report settings lower the Verbose setting.
Sorry I can't offer anything more practical as I don't have this function installed.
Ahh yes, sorry, I really need to learn to provide more detail when posting here!
I'm running Windows 10 Pro, 1511, waiting for them to work the Anniversary edition out.
Avast Premier (Paid) 12.3.2280 (build 12.3.3154.6)
It would be nice to know, eventually, if I can re-enable that feature, but with a (rolling? ever-expanding?) 2GB log file, it probably needs a little work.
If the log file settings are set to high verbosity by default, that's probably not good behavior. Could just be a bug? Perhaps they released it accidentally with that specific settings file? Might be nice, eventually, to have more Advanced settings available under each Avast module. I know not everyone likes advanced options, but it's nice to have them when you need them - without having to edit a flat-file, which can be challenging for the average computer user.