Via John Gruber’s Daring Fireball, I found the following from 9to5Mac:
An increasing number of people are finding a wide range of websites — including ours — are asking permission to allow downloads to your Mac from googlesyndication.com …
The problem is a rogue ad that has made it through to the Google ad network, which is used by a great many websites. If you do allow the download, it’s just a harmless text file, but it’s annoying to have to keep hitting Cancel to block it.
Another good reason to have an ad-blocker installed — my installation of uBlock Origin in Firefox already has the Google Syndication domain blocked.
Incidentally, I’m not linking to the 9to5Mac article because that site is packed with advertising and trackers, and one of those is… Google Syndication.