You didn’t do anything different, you didn’t ask for this. However the tech who cleaned your computer says that you had to accept the virus or click on something that permitted it on your computer. Suddenly every one is a suspect, you know you didn’t do it, so who did? Mostly likely it was you, you just didn’t know it. You might have been clickjacked. Clickjacking is taking some hidden code and putting it into an innocent looking webpage. Usually they tell you that you are doing something innocent or getting some info you need, or a link that looks like one you would normally use. That link is a lie, it is the permission that puts the virus onto your computer, and you never know it.
So what can you do? Some anti-virus stop these kind of attacks like AVG. But nothing is bullet proof. You need to be careful when you are browsing, make sure that you are on the site that you think you are, and don’t click on links that seem suspicious to you, or that make ridiculous offers that you are tempted by. If they do trick you and a virus gets through, don’t start looking at everyone suspiciously when the Tech tells you someone clicked on something they shouldn’t have. It was probably you.