Pre-installed virus
In most cases, Chinese factories - where many companies have turned to keep prices low - are the source. So far, the virus problem appears to come from lax quality control - perhaps a careless worker plugging an infected music player into a factory computer used for testing - rather than organized sabotage by hackers or the Chinese factories.
Ref. https://www.usatoday.com/tech/news/computer..._N.htm?csp=tech