In Nintendo's case, a line in its policy specifically said using "products not sold or licensed by Nintendo" with its products would void the warranty.
In a statement, Nintendo of America said it has changed its policies after review. “We have updated our warranty text to clarify that Nintendo provides warranty service for defects not caused by the user or by other unauthorized acts," the statement said.
The FTC declined to comment. The agency said in April that it had sent letters to six unnamed companies. A later report from Motherboard revealed, through a Freedom of Information Act request, that those firms were Nintendo, Microsoft, Sony, HTC, Asus and Hyundai.
The letters said the agency would review the policies again in 30 days, and it reserved the right to pursue legal action and seek "appropriate" remedies.