please help me security issue

[kandhro]

Hello friends
this was never happened before with me , even exactly i dont have right words to express the problem
my forum was working fine all of sudden i seen some text like error on my screen while i was browsing my forum
here is the screen short
1

i tried to open my forum site in a new tab , in the browser i seen a pop up to install the missing plugin/addon
it was installed some thing from/in java
after i tried to browse my forum every time i see the pop up like shown in screen short 2

this all not looks normal happened i think , please can any budy guide me what exectly happened ?
iam unable to browse my forum , how can i set it back to the normal ?
and what could be the safety precaution for above ?

Hope to have a guide .. Thanks & Best Regards