Google has discovered that Russian operatives bought ads on YouTube, Gmail, and the company’s DoubleClick online ad platform during the 2016 election, according to a Washington Post report.

Sources “familiar with the company’s investigation” told the Post that Google has found tens of thousands of dollars of online ad spend across virtually all of Google’s major platforms, including the company’s search, email, and online video service.

The ads appear to have come from a different source than the Russian-bought ads recently uncovered by Facebook. Those adverts, which were targeted toward 10 million of Facebook’s most susceptible customers, were bought the the Internet Research Agency, a Russian-backed troll farm. The Google ads appear to have a different origin, and the Post‘s sources say that Google “is still sorting out whether all of the ads came from trolls or whether some originated from legitimate Russian accounts.”

Online ads have become a hot topic in the investigation into Russia’s meddling in the 2016 election. Facebook’s discovery of Russian-bought ads on its platform has caused other tech companies to ramp up their own internal investigations, and thrown tech companies into the bullseye of congressional investigators. Facebook and Twitter executives are due to appear before congressional investigators next month, and there’s a good chance now that Google might be joining.