According to Twitter product manager Somas Thyagaraja…

Every day, millions of people send Direct Messages to communicate privately with friends, family, experts, brands, and anyone else they find interesting on Twitter.

In fact, we’ve seen the number of messages sent grow over 60% in 2015. And the number of Tweets shared privately has grown even faster, at 200% in just the second half of last year.

In other words, a growing amount of the conversation and sharing activity on Twitter is taking place away from public view, where it can be monitored and analyzed, meaning that Twitter is increasingly doubling as a dark social channel.

The good news: brands can benefit as Twitter gives users more flexibility to engage in private conversation and sharing, and encourages this behavior through additions like the new Message button.

The potentially not-so-good news: as with other large dark social channels, brands will need to be more thoughtful about how they track activity on Twitter to ensure they understand how fruitful their campaigns are.

Retweets, while still an important metric, don’t tell the full story of sharing on a platform that is increasingly home to private sharing activity.

Because of this, brands will need to engage in deeper analysis if they want to track content sharing on Twitter.

For example, for tweets that include external links, brands may find it useful to compare traffic attributed to Twitter to public retweet activity to identify tweets that are likely being shared in higher numbers privately.

Obviously, higher-than-expected traffic from a tweet that was retweeted by users with fewer followers could suggest more private sharing.

Overall it might be impossible for brands to monitor private sharing in a fully accurate way unless Twitter eventually offers analytics tools for this purpose.

But if brands don’t at least attempt to identify this activity they could be left with an inaccurate understanding of how their content is being distributed, which could in turn lead to misguided strategy and content marketing decisions.