Which is the safest online trading app?

Could you please elaborate on what factors one should consider when determining the safest online trading app? Are there any specific security measures that a reputable app should have in place to protect user funds and personal information? How does the reputation of the app's developer or company play into the overall safety of the platform? Lastly, are there any red flags or warning signs that users should be aware of when researching and selecting an online trading app?