Application Support permissions changing and hanging processes

Question

I'm running OS X 10.10.1 on a MacBook Air (11-inch, Mid 2013; 1.7 GHz Intel Core i7; 8 GB 1600 MHz DDR3; 500 GB SSD). For the past few weeks, several applications have been freezing up regularly. In particular, Evernote and Keyboard Maestro have been the worst culprits. I found myself having to constantly force quit these and other applications and processes. I also noticed that, periodically (that is, several times a day), my ~/Library/Application Support directory becomes world-writable, for no apparent reason.
It turns out that these problems are related because, if I chown -R and chmod -R go-w the directory, everything runs smoothly for a while. However, the permissions have been reverting back so often, that I ended up creating a cron job that runs every 20 minutes, which fixes them. This works (i.e., nothing hangs, and I can use my computer without problems), but I would rather not have to do this, and I would really like to know *** could be constantly changing this directory's permissions to 777. I've run a deep virus scan using Bitdefender, so that (hopefully) rules out something sinister.
Any advice would be much appreciated. Thanks.

Answer 1

Thanks for your reply.
I only installed the free version of Bitdefender (which runs on demand only, and not in the background) a couple of days ago, to rule out malware, so it can't be the cause of this.
I'm chowning to my user account, the owner of the home directory. Since my post, things have got worse (e.g., processes are hanging again, and TextMate won't even start), so I'm considering a clean install of OSX.