ExtremeTech's parent company Ziff Davis (also geek.com and pcmag.com) accounts:

- http://news.ycombinator.com/submitted?id=russellholly

- http://news.ycombinator.com/submitted?id=mrsebastian

- http://news.ycombinator.com/submitted?id=adeelarshad82 (their social media marketing manager, according to LinkedIn)

- http://news.ycombinator.com/submitted?id=11031a

Then there's the mystery of:

- Maxko87's (now hellbanned) autosubmitter for ExtremeTech: http://news.ycombinator.com/item?id=4441016

- evo_9 who heavily submits stories, about 50% of which are extremetech.com: http://news.ycombinator.com/submitted?id=evo_9

- ukdm who heavily submits stories, about 50% of which are geek.com: http://news.ycombinator.com/submitted?id=ukdm

TechCrunch I think is as simple as YC startups going there and then propping each other's articles up.

The Atlantic I'm not sure about, but they did just get busted spamming Reddit so I wouldn't be surprised.

GitHub probably has high double-digits overlapping users on a site like this, I doubt they need to do anything nefarious.