Is a Muslim's concealing of his flaws, which demonstrates his uprightness to others, considered hypocrisy and dissimulation?

A Muslim's concealing of his sins and not publicizing them is not hypocrisy or pretense; rather, it is legally mandated and considered a praiseworthy form of modesty that may lead its owner to repentance, in accordance with the Prophet's (peace be upon him) saying: "All of my Ummah will be forgiven except those who publicize their sins." As for one who shows people that he is doing righteous deeds while he has not done them, he is blameworthy and falls under severe warning.