Indian companies with large offices in US (Tata, Infosys, Wipro etc.) bring to US and employ people on tourist, educational and business visas. This happens frequently and it is a part of the business model for them...
It is illegal, but untraceable, because they are paid from the Indian offices to their Indian accounts. They are usually brought for short assignments and paid $15/h or less - for testing roles some resources get less than five bucks per hour...