Opening local word documents make network query

Dear friends,

Recently some users in our company network has started to complain that when they open some words documents, the system gets down and they wait 50 seconds for the document opening.
I?ve tested their computers and I saw following things: ?When you open the word document it queries to the network, the network traffic of computers become overloaded (document is not located on server or in network drive). I assume that it?s Trojan or spyware and I?ve scanned computer using 2 different antivirus program. Symantec and Kasperskiy, both of them couldn?t find any thing. In our network we use ISA as a firewall and all the unused ports a closed,

Do you have any advice how can I get rid from this problem.