For years, the Chinese government has owned a substantial portion of Lenovo (28% as of 2006[1]). It's no secret that the Chinese government attempts to hack US firms[2].
Although I have no direct evidence that the Chinese government has installed backdoors/monitoring/etc. into Lenovo laptop hardware, I think there is much circumstantial evidence to warrant serious concerns. So much so that the U.S. government is restricting access to Lenovo computers[3].
I'm at a place with Lenovo laptops that I was with Kaspersky anti-virus[4]. Although it might arguably be easier to install nefarious stuff into software, why take chances with your hardware?
[1] http://news.bbc.co.uk/2/hi/americas/4997288.stm [2] http://www.businessinsider.com/china-hackers-us-companies-gi... [3] http://freebeacon.com/national-security/military-warns-chine... [4] https://www.usnews.com/news/business/articles/2017-09-14/con...