Website blocked in Opera but not in IE? Help!

Hey guys. My dad clicked on a spam email (accidentally, it really looked like it came from a relative, I checked it), and there appeared to be a spammy link there. The link opened just FINE on IE, but what alarmed me so much- Is that the link was blocked when I used a different browser- Opera. Now, my question is- If it happens again, how can I be sure that Im not infected?

PS. I still dont know but my stubborn dad is not willing to use Opera. Its useless to convince him to use anything but IE.

 

What version of ESET security are you currently running on his computer? Have you already run an on-demand scan to check for infections?

 

Im running the latest ESS smart security module. Everything is updated to the last signature.

Ive ran about 10 scans since this happened- Nothing was found. Its still alarming that the same website which was blocked in Opera was passed fine in IE...