Hi All. Is it possible to hack into a wireless network when it has a security code?

In my house we have two laptops and one main PC (you know the 'tower' type).  I'm not very IT savvy by the way!   A few months ago my laptop was running very slow and kept freezing. I ran a virus scan but found nothing.  On my internet search history i found some very dubious websites not visited by me.

 

Nobody in our house has access to my laptop as it has password access but we do run off a wireless network in the house. My partners laptop and tower PC were unaffected and internet search history showed nothing dubious.  At the time this happened my norton had expired (i have since reinstalled)  and now have no issues.

 

My concern is could it have been possible for someone to have accessed our wirelessnetwork (we don't run it open either) and used my laptop as some sort of proxy to go on the internet?

 

i am at a loss as for any other explanation as no one has access to my laptop other than me and there is no way anyone could know the password as it is complicated and not written down anywhere.

 

As i said since installing norton i have had no further issues and everything is running fine.  Thoughts would be much appreciated please.