In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
Muslim families have the greatest responsibility in ensuring that they save them from being brainwashed from extremist groups and from those who preach agnosticism and atheism and secular fundamentalism.
Youth and adults become confused by exposure to self-styled teachers who do not have authentic Islamic knowledge and therefore do not follow the organic Islamic method of gaining or imparting knowledge.
This is one of the greatest sources of fitnah (seduction) in the modern world as there are no shortage of those who have been brainwashed by the self-styled teachers or scholars who pose as experts.
They mislead themselves and others. So, we must be ever on guard against all sources of fitnah, and pray to Allah to inspire us to be steadfast on the straight path. Here is a Du’a for us to read regularly:
Rabbanaa laa tuzigh qulubanaa ba’da idh hadaythanaa wa hab lanaa min ladunka rahmathan innaka antha al-wahhaab
(Our Lord, do not cause our hearts to veer off the straight path after You have guided us aright. And grant us mercy. You are the dispenser of mercies.)
Almighty Allah knows best.