What would be the best WiFi security software?

Hiya ya all.
I was wondering what you people think is the best WIFI network blocker? I have PC-Cillin that i am trying out but it keeps saying I have people on my network; tho, there is a red “X”. Are they actually still on my wifi? I have an Acer Aspire 5630 XP Pro mediacenter.

Btw, i am a newbie to the site and I really am liking this one so far.

HAG1 all.

Thanatos