Porn is often the cause
Recently called out to a slow PC, in a old chap's home, with lots and lots of pop-ups. Some porn, some dating, some virus warnings. All Chrome push notifications.
The cause was obvious, loads of porn tabs and granny dating going on. A quick cleanup - removing notifications and clearing the history/cookies/cache - sorted that all out.
That wasn't the most notable part though.
The next time the guy saw me, he 'told me off' for looking at porn on his PC. I was very confused, I'd never use a customer's computer for that. I'm a professional.
His reasoning is that he's now getting pop-ups for teens in his home town wanting to meet up for sex.
Biting the hand that feeds IT
