U.S. authorities said on Wednesday they had seized more than 350 websites selling gun silencers and parts from China used to covert semiautomatic pistols into fully automatic machine guns.

Federal prosecutors in Boston said the seizures followed an investigation since August 2023 into websites, businesses and people offering to illegally sell and import machine gun conversion devices.

Law enforcement conducted undercover purchases from those websites of gun-related items, resulting in shipments from China of packages that falsely described their contents as containing materials like a "necklace" or "toys," prosecutors said.

In fact, the packages contained machine gun conversion devices known as "switches" and silencers that are prohibited from being imported under the federal National Firearms Act, prosecutors said.

Many of the websites sold counterfeit goods and misused gun manufacturer Glock Inc's trademark to suggest the switches were produced by the company when they were not, authorities said in court papers, opens new tab.

"The seizure of these domains is a critical step in disrupting the flow of dangerous contraband that threatens public safety," Acting U.S. Attorney Joshua Levy in Massachusetts said in a statement.

Over 700 machine gun conversion devices, 87 illegal suppressors, 59 handguns and 46 long guns have been seized as a result of the probe, in addition to the 355 websites, said Ketty Larco-Ward, inspector in charge of the U.S. Postal Inspection Service's Boston Division.

"The proliferation of readily available devices which allow the illegal manufacturing of machine guns is a plague on our communities," she said.