In what’s being called “the biggest art scandal in a century,” French police are investigating about $255 million worth of paintings attributed to Old Masters that they suspect are forgeries.

The scandal could very well ruin the reputations of the experts who originally authenticated the paintings. One of the artworks being investigated, “David Contemplating the Head of Goliath,” attributed to Italian master Orazio Gentileschi, was recently featured in the exhibition Making Colour at London’s National Gallery. Though the full scale of the forging operation remains unknown — a list of about 25 suspected forgeries is reportedly expected to be released soon — one dealer dubbed the creator of these very convincing knockoffs “the Moriarty of fakers,” according to the Daily Mail.

“This is the biggest art scandal in a century,” art dealer Bob Haboldt said. “There has been nothing like this since the ‘early Vermeer’ scandal of the 1940s [when experts doubted the authenticity of a number of pictures by the Dutch master]. It has put an entire generation of dealers on alert. The careful marketing of these highly sophisticated forgeries using primarily older materials has caught the market by surprise. The implications will be that buyers will insist on more guarantees, scientific and financial.”

A French judge launched the investigation after a painting attributed to the artist Lucas Cranach the Elder was seized from an exhibition in March. “Venus,” allegedly dating from 1531, was sold by London’s Colnaghi Gallery in 2013 to the Prince of Liechtenstein. Though several specialists claimed it was a Cranach, others expressed doubts about the condition of the paint, the signature, and the winged dragon from Cranach’s family seal next to it, as well as the state of the wooden panel. Now, the Louvre is assessing its authenticity.

When the Cranach was seized, experts warned that it could be one of several forgeries of 16th- and 17th-century paintings recently sold on the London art market. Also under investigation is an £8.4 million (~$10.6 million) portrait attributed to Dutch Golden Age painter Frans Hals. The American collector who had purchased the painting from Sotheby’s forced the auction house to take it back and reimburse him. Sotheby’s is now contemplating legal action against London-based Old Masters dealer Mark Weiss, who was the source of the purported Gentileschi and Hals paintings. According to the Daily Mail, many of the suspect paintings passed through the hands of one Giulano Ruffini, a septuagenarian French collector.

The case is an example of how disturbingly sophisticated modern art forgery techniques have become, in part thanks to technologies like digital scanning and ubiquitous high-resolution photography. We’ve long left behind the era when expert eyeballs alone are enough to authenticate an artwork. “The works are difficult to detect as forgeries,” Haboldt said, “but they lack any credible provenance and references in the numerous publications about these artists. The latter should have made the principal dealers suspicious.”