Facebook, one of the world’s biggest social networks, announced it is filing lawsuits against online scam groups. Four Vietnamese individuals named N.H. Thêm, L. Khang, N.Q. Bảo, and P.H. Dũng have been accused. They allegedly used a “cookie theft” technique to hack into accounts of employees at advertising agencies and then ran unauthorized ads.

These four used a scam method by tricking victims into installing an Android app called Ad Manager for Facebook. This app illegally collected users’ login info, then accessed their Facebook accounts to run ads without permission. The app has since been removed from Google Play.

Even more notably, these four ran ads promoting the scam app itself. Facebook revealed that victims lost up to 36 million USD. The social media giant has refunded victims and strengthened security measures to protect user accounts.