If you are looking for antivirus programms for free then I have some suggestions for you:
Avast Free Antivirus (including a network scanner, secure web browser and other useful functions)
AVG Anitvirus Free (known for his good pishing protection)
Avira Antivirus (good in blocking malwares)
You are using a four years old version of Opera in a a OS whose support ended six years ago. I guess there is a high chance that it may be the cause of the problem.
@leocg Yes I thought that might have been a problem because it happens on a couple of other browsers as well.
But many thanks for your assistance, it is appreciated.