By Marcos Colon

Ad-revenue generating malware reportedly spread by a Chinese digital marketer hasn’t infected as many computers as previously reported, Microsoft says.

Allegedly discovered by security firm Check Point Software Technologies, the company reported on June 1 that as many as 250 million web browsers were infected worldwide, and 20% of corporate networks.

In a report published on Thursday by Microsoft titled “Understanding the true size of ‘Fireball’,” the company disputed those claims.

“So when recent reports of the ‘Fireball’ cybersecurity threat operation were presented as a new discovery, our teams knew differently because we have been tracking this threat since 2015,” Microsoft said in the blog post. “While the threat is real, the reported magnitude of its reach might have been overblown.” Instead, the company believes that the number of infected computers is at least 40 million, according to a Threat Post report.

The malware’s modus operandi is to hijack browsers and generate ad-revenue for Rafotech, a Beijing-based digital marketing agency.