The tech Cold War between US and China is running hotter than ever since the US blacklisted dozens of Chinese tech companies, including Huawei, from doing business in its country.

Meanwhile, US tech companies have been largely banned from doing business in China for years. Communist-ruled China has long maintained strict regulations on which websites and social media platforms are accessible in the country — and which are blocked behind China's so-called "Great Firewall" of internet censorship.

That ban prevents companies like Facebook, Google, and Dropbox from reaching the country's over 800 million internet users. Just this week, Apple removed two apps from its App Store that are seen as potentially offensive to China. An app called HKMap Live, used by protesters in Hong Kong to track police activity, was removed after Apple said it was being used to "target and ambush police." Additionally, the US publication Quartz had its app removed from Apple's China App Store and blocked in mainland China.

Despite the ban, China still factors into the equation for US companies: Facebook, for example, saw an estimated $5 billion in ad revenue from Chinese-based companies in 2018, making the country the company's second largest ad market, according to AdAge.

That "firewall" isn't impenetrable, either, as some Chinese citizens have found ways to circumvent blocks on websites by using virtual private networks (VPNs).

Here are the all the major US tech companies that are blocked from use in China, according to censorship tracker Great Fire: