At least 10,450 Instagram accounts have popped up over the last four months selling masks used around the world to protect people from the deadly virus, according to a report from social-media research firm Ghost Data.

The “dubious” accounts are predominantly based in China, field inquiries through WhatsApp and take payments over PayPal to move their stock, researchers say. The sellers have proliferated even though Facebook — Instagram’s parent company — banned advertisements for masks about a month ago.

“There are no guarantees that advertised products are genuine and safe, not to mention the possibility of health and safety threats for a potential buyer,” Ghost Data researchers wrote in their Monday report, which was first detailed by The Wall Street Journal.

The firm identified a total of 25,861 Instagram posts selling medical masks and said the number of posts exploded along with the pandemic. The accounts used hashtags to promote their wares such as “#surgerymasks” and “#n95,” a reference to the type of respirator mask used by health workers, the researchers found.

The sellers largely hawked masks made by 3M, whose brand appeared in nearly 85 percent of the posted images, according to Ghost Data. The Minnesota-based manufacturing giant — which President Trump recently ordered to produce N95 masks — warned last month of an increase in counterfeiting of its products.

E-commerce companies such as Amazon and eBay have also battled suspect merchants amid concerns about price gouging. eBay has banned listings for health-care masks, and Amazon pulled more than 1 million fake and overpriced products from its marketplace in February.

But those platforms also have screening protocols for sellers, making Instagram more attractive for those looking to move masks under the radar, according to Ghost Data.

Facebook is tackling the accounts Ghost Data identified in addition to removing millions of ads and commerce listings for masks, coronavirus test kits and other vital supplies, a company spokesperson said. The social-media giant has also cracked down on content that promises to cure the virus or spreads conspiracy theories about the disease.

“We’re focused on preventing exploitation of this crisis and have removed many of the accounts and blocked many hashtags included in this report,” the Facebook spokesperson said in a statement. “We use several automated detection mechanisms to block or remove this material from our platform.”