Want to be open to all direct messages? Twitter will let you

A new direct message button will appear on the profiles of Twitter users who let others send them private messages.

As part of Twitter's larger push to give more people a reason to use its service, it is changing its direct messaging function to let users receive missives from people they don't follow.

Previously, users could only send the private, direct messages to those who followed them. By letting more users message each other privately, Twitter hopes to more strongly compete against messaging apps WhatsApp, with roughly 800 million monthly users, and Facebook Messenger with 600 million users who log in monthly. Twitter had 288 million users as of the end of last year.

Importantly for those who worry about spam and abuse, Twitter is letting would-be recipients of the DMs decide if they want to change their account settings to accept direct messages from people they do not follow. A new direct message button will appear on the profiles of people who turn this on.

As part of the change, Twitter users can directly reply to anyone who sends them a direct message, regardless of whether that account or person follows the user.

The changes are rolling out globally starting Monday for all Twitter users.

Not everyone applauded the change, with some pointing out it might flood some users' accounts with spam from companies on Twitter.

"It's an 'upgrade' for brands that want to 'engage' users who don't want to hear from them," said Fatemeh Khatibloo, an industry analyst at Forrester, in a tweet.

Zach Miners covers social networking, search and general technology news for IDG News Service. Follow Zach on Twitter at @zachminers. Zach's e-mail address is zach_miners@idg.com