how do you remove a device listed in NIS security map?

NIS 2011
Vista Home premium 32 bit

OK during holidays, some one visitiing used my wireless connection for thier iPad.
I was not happy about this since thier iPad had no security product installed.

so anyway, now this iPad shows up as another item in my network security map, even though they (iPad owners) are gone
Two questions;
1 how do I remove the item from my network security map?

2. Does the fact that thier iPad had no security product put my Network at risk GOING FORWARD? Like is my wireless password and IP on there iPad and can that be taken from thier to enter my network in the future?