One by one, the major online services are all adding two-step verification. Twitter has just joined the crowd (including Apple and WordPress most recently) that has recently added the option for people to put a second verification step on their accounts. You can find this option on your settings page if it's available to you, as this seems to be a gradual roll-out.
There's a couple potential problems with Twitter's implementation, as it currently stands, due to one simple rule:
- One phone for one account
If you have multiple accounts and only one phone to associate with it, you'll have to pick which account you wish to secure with additional authentication. Likewise, if you have a business account that's used by multiple people, only one person with one phone number can perform the authentication.
So as far as it goes, this is a very limited implementation of two-step authentication. While it's certainly better than nothing, this is likely to help a fairly small percentage of Twitter's user base. With these limitations, the recent high-profile Twitter account hacks of news outlets and businesses would not likely have been prevented with this additional security. While Twitter is recommending that people access their accounts with only one computer per account, this isn't feasible for a lot of organizations.