The way I understand CC licensing, they could take your entire feed if they met the two requirements you've provided:
1. Attribution
2. Noncommercial

I think that the membership request does make it appear to be their work rather than yours, which at least skirts the edge of attribution.

I don't see anything on HCI's website which says that they are a nonprofit group, so I assume that they are making money. That means they are definitely violating the terms of your license.

They can link to you, like a real blog roll, and give you additional traffic. :) They can quote you, as long as they make it clear that you wrote it. What they are doing right now is exactly what you called it: stealing.

People don't have a clue about licenses for online content. Personally, I don't think that CC licenses are that hard to understand. Copyright and fair use are confusing, so I can forgive people for that. But I've caught too many SMEs--many with PhDs--copying and pasting content from online sources to think that most people have even a passing understanding of copyright. Whoever set this up at HCI may just be clueless rather than malicious, so you might try contacting them to see what happens.