In a company blog post, Twitter said the increased number included interactions they hadn't previously considered: That 1.4 million encompasses users who retweeted, quoted, replied to, mentioned, or liked those accounts or content produced by them during the 2016 election. (It also includes those who opted out of email notifications and weren't included in Twitter's initial wave of outreach emails.) The social network pointed out that this tally still doesn't include every user ever who was exposed to messages from the Russian-backed accounts -- for example, those who saw their tweets but didn't otherwise interact.
But it's worth pointing out that Twitter didn't expand its pool of spam producers -- it's still only considering content from the 3,814 accounts linked to the Russia-backed Internet Research Agency (IRA) that it had previously suspended. The social network will reach out to those in the revised 1.4 million total who it hadn't already emailed.
But as Ars Technica reporter Cyrus Farivar noted in a tweet, the social network duly informed him that he'd interacted with a Russian-backed account...but didn't identify which one, nor any details about the interaction. Which calls into question how useful these outreach efforts really are for informing users so they can avoid such accounts in the future.