I've noticed this a couple of times but actually managed to find out what was causing it today. I'm on a university halls LAN (wired) connection - 10Mbit up/down and have sometimes noticed very high internet usage in Activity Monitor despite me not really browsing that much. When I noticed the Data Received was about 500Mb greater than it should have been and there was a steady 50 - 65Kb/sec stream of data being received even when no apps were using a large amount of bandwidth, I went investigating. After quitting all applications and anything that might use the internet (including rebooting the dock & dashboard), I somehow came down to the SystemUIServer process in Activity Monitor. Quitting this (with it instantly restarting, as expected) stopped the steady flow of network traffic in and things went back to their usual idle. Is this common for SystemUIServer - I've only noticed this a couple of times? Should I look into things more closely, and if so, where should I start looking? Is there any way to stop it from doing this, as obviously I don't want my network admins coming down on top of me for using excessive bandwidth (they are very strict on P2P and have been disconnecting a lot of people for excessive filesharing and are starting to disconnect people who even just have P2P software installed on their computer but never use it) Thanks for the help Edit: Sorry, forgot to mention: I'm using OSX 10.4.5. Applications used today include Dashboard, Mail, Safari, iTunes, Adium, DVD Player, Word and Excel.