Bold red arrow appeared on my screen, doesn't go away

[Android Central Question]

It's a red arrow, outlined in yellow, at the upper left corner of the screen. If I tap on it, it expands, and a message appears: "Write down a name and number," followed by a camera icon and a (fake) whatsapp icon. It definitely looks suspicious. The arrow can be collapsed so that only the arrowhead shows, but it doesn't go away, it stays on top all the time. I didn't enter any data, but I can't get rid of it either, and I've found no information about it. I scanned my phone for malware, and nothing was detected.

 

[belodion]

Does it persist in Safe Mode?

 

[yochruth]

I don't know how to put my phone in safe mode. I searched the user manual for "safe mode" and it isn't found. It's a Samsung A5, 2017 model.

 

[yochruth]

I tried Airplane Mode, and for a second the arrow was gone, but then it reappeared.

 

[belodion]

Long-press Power, as if to power off, then long-press the "Power off phone?" message box. The option to boot into Safe Mode will then appear, unless I don't know my Samsungs (I don't in fact, but that is the normal method).
If the trouble stops in Safe Mode, a third-party app is causing the trouble. Find it, then Clear Cache, Clear Data, Force Stop and Uninstall.
Optionally, add an app review comment.

When finished with Safe Mode, reboot the phone to return to normal.

Welcome as a new member, and if that doesn't fix it, let us know.

 

[yochruth]

Right, I started the phone in Safe Mode according to your instructions, and the "thing" doesn't appear now. Now I have to try to find the app that's causing the trouble.

 

[yochruth]

It worked! Thank you very much for your friendly welcome, and for you help. Actually all I did was clear the data from an app that I thought might be the source of the trouble, and then I rebooted to normal, and it was gone.