- Google 2-Step Verification
- Facebook Login Approvals
- Instagram Two-Factor Authentication
- Twitter Login Verification
- Apple Two-Step Verification
- Microsoft Two-Step Verification
- Yahoo Second Sign-In Verification
- Evernote Two-Step Verification
- Dropbox Two-Step Verification
- LinkedIn Two-Step Verification
- Snapchat Login Verification
- PayPal Security Key
- Square 2-Step Verification
- Venmo Verification
- IFTTT Two-step Verification
- MailChimp Two-Factor Authentication
- Kickstarter Two-factor Authentication
- WordPress.com Two-Step Authentication
- Tumblr Two-Factor Authentication
- Amazon Two-Step Verification
- Sony PlayStation 2-Step Verification
- GoDaddy Two-Step Authentication
- Dreamhost Multifactor Authentication
- TeamViewer Two-Factor Authentication
- LastPass Multifactor Authentication
- Dashlane Two-Factor Authentication.
- TurboTax Two-Step Verification
http://www.pcmag.com/article2/0,2817,2456400,00.asp