Have just finished a bit of research about this pop-up warning nuisance. We,ve commonly found 9 out of 10 ''your PC is at risk-to stop this happening again'' pop-ups are not the result of yours or a third partys security lapses, more a case that you will be forwarded to the software site that sent you the pop-up in the first place, and sell you a useless 'patch' or similar useless piece of software.
You may-not even be aware that you are being charged for these software downloads, and they should be completely ignored by closing the pop-up window top right x.