How does misinformation circulate on the social media platform? TikTok has been typically less critical of Russia than US-based rivals Facebook and Twitter; however, after Russia invaded Ukraine, the social media platform complied with EU sanctions by blocking users' access to Russian state-backed media. Most work on the dynamics and downsides of social media has focussed on Facebook and Twitter, with research demonstrating how misinformation has spread on those platforms. But TikTok's central role in spreading rumours about the Ukrainian war has had less focus. Tom Simonite discusses why it's so challenging to determine the platform's role in spreading misinformation and how the power and influence of its recommendation algorithm make it so difficult for outside researchers to assess its impact.