Cryptocurrency mining malware that infected over a million computers in China reportedly earned its creators more than $2 million over two years.

According to a local news report on Monday, police in China’s Da Lian city have arrested 20 suspects from a computer technology firm who allegedly gained control of the large number of computers in order profit from illicit cryptocurrency mining.

The hackers created and embedded the malware inside internet browser plug-ins they developed for various purposes, such as enhanced browsing speed, which were shown in display ads that reached 5 million computers in the country.

By clicking the display ads and installing the plug-ins, over a million computers were subsequently infected, mining a total of 26 million digibyte, decred and siacoin tokens over the course of two years, according to the police.

The hackers apparently opted to mine more minor cryptocurrencies since they don’t require such significant amounts of computing power, allowing the back-end mining process to be quieter and less likely to be spotted by victims.

The report also indicated the hackers developed a network of more than 100 agents to help propagate the illicit mining software, such as through working relationships with internet cafes.

The news follows a previous report in which another group of hackers was also busted in China for allegedly colluding with local computer maintenance firms to hack into over 100,000 computers owned by internet cafes – also to mine the siacoin cryptocurrency.

Computers image via Shutterstock