The FTC recently opened up about closed letters.  In a blog, FTC said that

Closing letters from the staff of the Bureau of Consumer Protection are just what they say they are. They’re letters from FTC staff telling a company or individual that we’re closing our investigation into their conduct. Closing letters aren’t binding on the Commission and the text of the letters makes it clear that the FTC reserves the right to take further action as the public interest may require.

The FTC adds that

there are a number of practical reasons why staff may close an investigation even when there is concern that a company has violated the law. That’s why closing letters also expressly state that the receipt of a letter shouldn’t be construed as a determination that there wasn’t a law violation.

Even though staff closing letters serve a narrow purpose, it’s still wise for businesses and attorneys to read them. They’ll often include a pointer that can help other companies with their own compliance efforts. Just be sure to read them on the Staff Closing Letters page on the FTC website. Why? Over the years, we’ve heard reports about companies falsifying or altering FTC documents – including correspondence, civil investigative demands, and even staff closing letters. If you see a closing letter anywhere other than on the FTC website, the best way to be sure you’re looking at a genuine document is to check if it’s published on ftc.gov.