That JavaScript extracts the hidden code out of the image and executes it ... the script will request the advertising banner. The server will reply with either a clean or a malicious version ...

Hackers hit CoinMarketCap and Cointelegraph with ad-based wallet scams. CZ warns users after $18K stolen from 39 victims via JavaScript exploits.

If your chosen Tumblr theme does not have built-in banner support, you can also upload a header to a third-party hosting location and insert the image using HTML code. Sign into your Tumblr ...