Question What are those white stains on the back of this GPU?

[marakaibo]

I've got this used GPU which has some white stains on its back. What are those? I've searched the web and from what I understand they could be flux residues but I'm not sure. Any other idea? Looks like this GPU was removed from a working PC and it was still functioning when it was removed. Then it sat in its own box for maybe a couple of years and now it was given to me. I've not tested it yet and I'm not sure if it's safe to power it on before removing that white stuff. Anybody knows what that is? Is it harmful? Should I worry? Can I leave it there or should I clean it even if the GPU works? I don't know when those white marks appeared, if the card was sold like that or if they appeared later during daily usage.
Thank you all for any help.

 

[Midwayman]

Flux seems reasonable

 

[Fallen Kell]

Yeah, pretty sure that is remnants of flux and the cleaning off of said flux. Typically flux will turn a dirty yellow/brown, but it is very likely some kind of oxidizer cleaning solution used to remove the flux that turned white.

 

[Stuka87]

What brand GPU is this?

Its been a whole since I have seen a PCB with residual flux like that. Almost looks like it was re-flowed or something.