What exactly is an ssl stripping attack? Am I secure?

Hi i connect to my wifi router from my Android when I'm home. About 45 minutes ago I received an alert from Norton that my wifi security was compromised and that there was an ssl stripping attack. ( I use eset, lookout, Malwarebytes, and a paid subscription to Norton) I turned off wifi and realized I wasn't connected to my personal router but to a no password wifi called xfinitywifi. I don't ever remember connecting to that network. At all. I was wondering what exactly is an ssl stripping attack and if I'm secure. I don't know what Norton does if anything to protect me. They say they do. But I have no idea right now and am worried. Thank you.