Mine was 5 years ago when I had only Norton Internet Security '06 version installed on my old xp pc. I was purely a novice when it came to internet security. I had never heard of Malwarebytes, Superantispyware, Hitman Pro, Spyware Doctor or any other scanners. I had numerous popups on the screen saying that I was infected and to "click here" to fix the problem. So I did click on one particular button which made the problem worse. I never knew what the infection was as I did numerous full scans with NIS, and it never found any malware etc.
I had to ring a Symantec tech to probe my pc from the otherside of the world (India, I think) . He found some malware and removed them, but unfortunately I had to re format my pc and so I lost everything and had to reinstall all my software.
The tech charged me about $230 to clean my pc
Once my NIS subscription ran out, I vowed never to use Norton and Internet explore again!