Alphabet Inc.’s Google concluded that the manipulation efforts began as early as January 2017, Kent Walker, head of global affairs, wrote in a blog post on Thursday. Google worked with cybersecurity firm FireEye Inc. to identify the accounts from Iran. “We can’t go into all the technical details without giving away information that would be helpful to others seeking to abuse our platforms,” Walker wrote in the post.

Google has faced less political fire than Facebook and Twitter for letting state-sponsored election meddling spread on its services. But US officials have identified ways that Russian-backed actors used YouTube as a vehicle for political influence. Walker is slated to testify before a Senate Intelligence Committee hearing about foreign election interference on Sept 5.

In the blog post, Walker also said Google removed 42 YouTube channels related to the Russian-based Internet Research Agency, which sowed discord on social media before the 2016 US presidential election. Midterm elections are coming up in November and tech companies are under pressure to prevent their services from being manipulated again.