Gmail IMAP server refuses connection

This isn't really a Mountain Lion question...this person just happens to be using 10.8.5

Helping a friend whose Gmail account got "hacked". I don't know the specifics, but once he realized someone had gained access to his email, he change the password via the web interface.

Since then, Apple Mail refuses to connect via IMAP. We've:

1) re-entered new password both in the onscreen prompt and in Preferences>Accounts

2) have zapped entry in Keychain and re-entered

3) have deleted the entire account, and re-added

All the while, web access works fine. His other Gmail account continues to work fine in Apple Mail.

Have looked at his Gmail security settings, but nothing apparent that would block IMAP. Two-factor authentication is NOT on. Also, checked his setting and IMAP is enabled.

Is there something a "hacker" could have done to create this scenario? Does Gmail, as a matter of course, block some IMAP accounts?