An analysis of the Google Fred update was published by Sistrix, an SEO toolset data collection company, after they reviewed “nearly 300 domains.” According to their analysis, the sites and pages were described as being hit like this:
“…advertisement, outdated, thin and scraped content, as well as incomprehensible articles made up of 300 word ‘SEO texts’ pumped to the brim with main keyword mentions and void of any useful information or a sense of readability.”
Sistrix confirmed Search Engine Land’s analysis of Fred, where they had said that low value content sites where hit by this update.
Juan Gonzelez from Sistrix had analyzed 300 websites domain from Google UK, US, Spain and Germany, all of which lost Google Search results visibility after March 13, 2017. According to Juan, “nearly all losers were very advertisement heavy, especially banner ads, many of which were AdSense campaigns … Another thing that we often noticed was that those sites offered little or poor quality content, which had no value for the reader.”
There where specific examples that he’d shared of sites that had been hit and how bad their visibility dropped. A number of them had lost between 50 percent and 90 percent visibility in Google. This correlates with what was seen when webmasters reported their Google traffic had dropped after being hit by the Fred update.
The following chart shows the ranking distribution on Google for freewarefiles.com before the Fred update:
This chart shows the ranking distribution on Google for freewarefiles.com after the Fred update: 
The following chart is a visibility chart by Sistrix shows a 75 percent drop for freewarefiles.com in Google .com:
It was confirmed by Google that there was a new update, but wouldn’t say anything else outside of the idea that what it targeted can be found in Google webmaster guidelines.