Gmail users can access their account on the official website or by using first-party or third-party apps and services instead. A first party app is for instance Google's official Gmail app for Android, while Thunderbird and the mail client app of Windows 8 are third-party apps.
Google announced back in April 2014 that it would improve the sign-in security of its services and affect any application sending usernames and passwords to the company.
The company suggested to switch to OAuth 2.0 back then but did not enforce it up until now.
If you open the new less secure apps page under security settings on Google, you will notice that Google has disabled access by default.
Note: You see the page only if you are not using Google Apps or have enabled two-factor authentication for the account.
Google states on it that "some devices and apps use insecure sign-in" technologies to access account data, and that the disable setting blocks these apps and services from accessing the Google Account.
You can flip the switch here to enable less secure applications again so that access is regained.
A help page lists some of the applications affected by the change:
How to resolve access errors
If you are receiving error messages -- password incorrect or similar -- when trying to sign-in to your Gmail account using a third-party application or service, chance is that it is affected by the change.
You have several options at your disposal to resolve the issue:
The easiest option, without doubt, is to switch to enable on the security settings page. Two-Factor authentication may improve the overall security, but since you may need to create app-specific passwords, does not seem to improve security when compared to switching the setting to enable.
It is possible that companies will start to update their applications and services to support Oauth 2.0 so that users don't have to make a decision in this regard anymore.
For now, the three options listed above is all that is available to those users.
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Ghacks is a technology news blog that was founded in 2005 by Martin Brinkmann. It has since then become one of the most popular tech news sites on the Internet with five authors and regular contributions from freelance writers.