"Employment of any kind is strictly prohibited (including volunteer work)." What if, I've always wanted the time to write or try some other hobby. And, maybe I create a 'blog' page with no goal of making money, just to keep busy. Then luck may have, I receive a small stipend for my efforts.  I can't imagine people just doing nothing, except eating, sleeping, or site-seeing.

That statement basically means formally working for a business, company or organization which would require a work permit.

What you do privately behind closed doors on a computer would not be a problem. It is a bit of grey area but many people are doing it.