THE STORY begins with a pair of Nike Air Max 95 shoes with neon-green soles. Russian Prime Minister Dmitry Medvedev was photographed wearing them; emails stolen from his iPhone by dissident Russian hackers show they, along with several other articles of clothing Mr. Medvedev has been seen in, were ordered online and delivered to an address linked to a web of companies and charities controlled by close confidants and relatives. After months spent probing the network, the Anti-Corruption Foundation, headed by opposition activist Alexei Navalny, has released a video and documentation it says show that Mr. Medvedev has accumulated more than $1 billion worth of property, including vast estates in Russia and Tuscany and two yachts.

Mr. Medvedev’s spokesperson shrugged off the story, as did the Kremlin. But as of Thursday, Mr. Navalny’s biting, often humorous and slickly produced video (in Russian with English subtitles) had been viewed 7.4 million times on YouTube and attracted 40,000 comments. It’s a testimony not only to the staggering corruption of the regime of Vladi­mir Putin, but also to the power of the Internet and social media to expose it and inform Russians about it.

Mr. Navalny guides viewers through a dazzling tour of Mr. Medvedev’s purported properties, recorded by drones that flew over the high walls surrounding the estates. A sprawling chalet in Sochi, site of the 2014 Winter Olympics, contains distinctive lampposts that appear in the background of Mr. Medvedev’s own Instagram photos. One of his yachts was photographed at the dock of his huge estate outside Moscow. In the Kursk region, home of Mr. Medvedev’s ancestors, another vast estate includes vineyards, as does a property in Tuscany.

Mr. Navalny’s conclusion is stark: “Medvedev can steal so much and so openly because Putin does the same, only on a grander scale; because everyone in government does the same, because the judges and the prosecutors and the special services are also doing the same. . . . The system is so rotten that there is nothing healthy left.”

The opposition leader, who shook up the Kremlin by leading street protests in 2011 and 2012 and capturing a reported 27 percent of the vote in Moscow’s 2013 mayoral election, appeals to Russians to do their part by sharing the video with friends and by signing petitions in support of his candidacy for president in 2018. It is doubtful that Mr. Navalny will be allowed to run in that election, presumably against Mr. Putin; that was the point of the recent criminal case against him. But the exposure of Mr. Medvedev — who has portrayed himself as a corruption-fighting technocrat — and the impressive online response to it offer hope that Mr. Putin’s regime can be weakened by the revelation of its crimes.

The Trump administration, which has been backed up by Russian propaganda outlets in denouncing reports on its own activities as “fake news,” can hardly be expected to assist courageous dissidents such as Mr. Navalny in exposing truths about the Kremlin. But other Western governments and nongovernmental organizations should do what they can to help. Disseminating evidence of Mr. Putin’s corruption would be an appropriate response to Russia’s disinformation campaigns in the West.