Gmail Check mail from other Gmail accounts (using POP3) Error

I tried using Gmail to check another Gmail account using POP3. The, I got email notification from them.

Sign-in attempt prevented.
Someone just tried to sign in to your Google Account from an app that doesn't meet modern security standards.

Details:
Saturday, February 13, 2016 7:22 PM (Eastern Standard Time)
United States*

We strongly recommend that you use a secure app, like Gmail, to access your account. All apps made by Google meet these security standards. Using a less secure app, on the other hand, could leave your account vulnerable.

Some users that user Gmail to fetch or backup another Gmail account experienced Gmail blocking Gmail with error in POP3 server. I also tried and get the error:

[AUTH] Web login required: https://support.google.com/mail/answer/14257

The solution is just simple, that is by "Allow less secure apps: ON".



They said that some non-Google apps and devices use less secure sign-in technology, which could leave your account vulnerable. You can turn off access for these apps (which we recommend) or choose to use them despite the risks.