how to see other people's facebook account on your computer network?

[Night_Wolf]

ok , a guy from work said he saw my face book account activities and he is not on my friend list
he said he downloaded a pc application that allows him to see other people who are using the network computers to see their accounts , emails , passwords , etc
I am very private person , is this true , and if it is
is there any programs to block such attempts or warn me from that ?
i want to block my pc from such programs
thanks
@$ayit - it is not like that , it is like he can see what is on my pc ( kinda like team viewer or skype desktop share ) , which there is no such programs on my pc.
@ Camille - he said he is using hacker programs , i have kasper Internet security on my pc installed , so it should gives me a warning or something if someone is trying to preview my pc
@ midnight - god i hope so , but he seemed pretty sure what he is talking about