Academic paper from last month’s International World Wide Web Conference for people who enjoy reading such things. :-)

*"Our approach involves injecting malicious Monero Tor hidden service nodes into the Monero P2P network to correlate the onion addresses of incoming Monero Tor hidden service peers with their originating transactions.

And by sending a signal watermark embedded with the onion address to the Tor circuit, we establish a correlation between the onion address and IP address of a Monero Tor hidden service node."*