I just ran a quick scan, after updating Avast manually, and it looks like everything is clear.
Thank you, Steven and Diddy, for helping me out on this.
Whilst I'm here, the main page of my Avast! says that I have 38 days of registration left. What will happen after the 38 days? I'm using the free version but I do vaguely recall registering something a while ago...I can't remember how I did it. Can I be proactive and re-register ahead of time? I can't find an option for doing so.