It would appear that some big name press release distribution sites have taken a hit in Google.
Sean Malseed at Seer Interactive pointed out that PRWeb lost over half of its traffic, and dropped out of the first 20 Google results for over 8,000 keywords, based on data from SEMrush.
"It looks like there’s guilt by association, as well," writes Malseed. "Bloomberg, who partners with the press release agencies to disseminate releases, also took a huge hit."
Barry Schwartz took things a step further and looked at Searchmetrics data for PR Newswire, PRWeb, BusinessWire, and PRLog, each of which took hits after the Google released Panda 4.0. It's unclear whether this was an effect of that Panda update or something else Google did.
Last summer, Google updated its guidelines for what it considers link schemes. This included, "Links with optimized anchor text in articles or press releases distributed on other sites."
In a Webmaster hangout, Google's John Mueller said Google wants all links in press releases to be nofollowed, and press releases should be treated like advertisements. He indicated that SEOs were using press releases more for search purposes.
The press release distributors have not been shy about promoting SEO value either.
A couple years ago, BusinessWire launched an SEO-enhanced platform after patenting its SEO strategy. Google is literally running an ad from PRWeb (pictured at the top) for press release SEO right now.
Images via PRWeb, Google