A file that Apple updated on its website last month provides the first acknowledgment that it's relying on Google's public cloud for data storage for its iCloud services.

The disclosure is fresh evidence that Google's cloud has been picking up usage as it looks to catch up with Amazon and Microsoft in the cloud infrastructure business.

Some media outlets reported on Google's iCloud win in 2016, but Apple never provided confirmation.

Apple periodically publishes new versions of a PDF called the iOS Security Guide. For years the document contained language indicating that iCloud services were relying on remote data storage systems from Amazon Web Services, as well as Microsoft's Azure.

But in the latest version, the Microsoft Azure reference is gone, and in its place is Google Cloud Platform. Before the January update, Apple most recently updated the iOS Security Guide in March.

The latest update doesn't indicate whether Apple is using any Google cloud services other than core storage of "objects" like photos and videos. The document also doesn't make it clear when Apple started storing data in Google's cloud. Microsoft declined to comment. Apple didn't respond to a request for comment.

Earlier this month Google said its public cloud and its G Suite line of cloud-based productivity apps contribute $1 billion in revenue per quarter. In the fourth quarter, market leader Amazon Web Services brought in $5.11 billion in revenue.

In addition to Apple, other Google public cloud customers include Kroger, PayPal, Snap and Spotify.