two-factor authentication system 双因素身份认证系统
two-factor system
双重系统
以上为机器翻译结果，长、整句建议使用 人工翻译 。
The "two-factor" verification system, which will be optional, asks users to register a phone number, e-mail account and six-digit code that would have to be entered, via text message, each time they log in to the site.
CNN: Twitter bumps up log-in security after hacks
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