In cooperation with the US Consumer Product Safety Commission, Lenovo has issued a voluntary recall for approximately 50,500 ThinkCentre all-in-one desktops citing a fire hazard. The affected models have a defective power supply that can overheat and, as at least one user experienced, burst into flames. Along with the single fire incident, another machine reportedly began smoking. No injuries have been documented and there's no mention of property damage (besides the flaming system, of course).
Unlike some all-in-ones that use an external brick, the ThinkCentres have an integrated power supply so Lenovo will likely have to send a technician to your home, or you'll have to bring/ship your machine to a repair center. That part of the remedy is unclear as the announcement only says affected users will have to "schedule an appointment," while the recall's FAQ page notes that Lenovo support will set up a "repair date" when you call. Regardless of how your system fixed, it shouldn't cost you a dime.
Lenovo says M70z and M90z ThinkCentres with manufacturing date codes ranging from 1001 to 1012, 1101 to 1112, 001 to 012 and 101 to 112 likely have the faulty component. The systems were sold online, by telephone and through Lenovo resellers between May 2010 and January 2012. The former models would've cost about $500 while latter units sold for around $800. You can contact Lenovo at 855-248-2194 or visit lenovo.com/aiopsurecall with your PC's serial number to confirm that it's affected.