high packet xfer when pc idle

Hello: I belong to another user group where an interesting question was asked. I don't have answer, so I'm asking youse.

When the PC is idle, the user comes back & sees data being transferred apparently over the net (he views the network icon is systray). He said sometimes packet size is as big as 250K. "Resetting" (his word) will temporarily fix, then the packets increase again in size, which he notices slows down his browser.

He asks (& so do I) is this a concern? He does have WEP.

I'm going to answer him that WEP is not secure, and to use spybot & adaware.

I also see on mine, that ZoneAlarm's little tray icon is fairly constantly signalling. Doesn't seem as big as his issue, but is it the same idea only different, like ZA is routinely pinging & getting pinged by my PC & outside, to check the connection (DSL)?

What do youse think? Thanks.