Years ago call center work was done from an office building. Most call center were legit providing a useful service. There were some however that was hard selling people into buying a product or service that was useless or did not exist. You would find companies like this on free job boards such as Craigslist or Backpage. The smarter one would advertise on paid services such as Monster.com to make themselves look legit.
When the economy crashed and technology got better businesses started hiring people to work from home. People would log onto a dialer system and make and take calls from their house. Companies could use these dialer systems to keep track of their workers. They could see when they were logged on and on and off a call. This way no one could lie and say they were working when they weren't.
This also gave the chance for smaller companies without the overhead to afford rent at a building to start up. They place ads online looking for people to work from home. A lot of the time the owners of the companies even work from their houses. This also gives the companies a chance to scam both their workers and customers much easier. I can't tell you how many times these work at home companies turn out to be scams. Not only do they provide a useless service but they don't pay their workers for selling this useless service.
The term Boiler Room is a call center that engages in shady activities. Well this time they have access to people all over the world to make these calls. They aren't just calling from one place anymore. This makes it harder for these companies do be shut down. Then when the companies bad reputation gets out the owners simply change the name. Make sure you do your research before dealing with a company you have not heard of.