Google blocks sign-in attempt from ChatSecure

[contrapunctus-1]

I received the following email from Google when I tried to add my Google account in ChatSecure (the account addition in the app was stuck on 'logging in')

Review blocked sign-in attempt

Hi ,
Google just blocked someone from signing into your Google Account from an app that may put your account at risk.
Less secure app

*
Don't recognize this activity?
If you didn't recently receive an error while trying to access a Google service, like Gmail, from a non-Google application, someone may have your password.

[SECURE YOUR ACCOUNT]

Are you the one who tried signing in?
Google will continue to block sign-in attempts from the app you're using because it has known security problems or is out of date. You can continue to use this app by [allowing access to less secure apps], but this may leave your account vulnerable.

Best,
The Google Accounts team
*The location is approximate and determined by the IP address it was coming from.
This email can't receive replies. For more information, visit the Google Accounts Help Center.

I'm not sure why they call it a "less secure app.", or whether anything can be done to mitigate this. Just putting it here for the sake of information.

Thank you for ChatSecure!

PS: perhaps https://guardianproject.info/howto/chatsecurely/ should be updated to reflect this, among other things?