Jeanny, a T1 and T3 are satellite connections with huuuuuge bandwidths. What you should also know though is that your regular Joe can't afford a T3, so those that have them are prolly people sharing from work or organisations who deliberately go with the tempting T3 and spread fake files and whatnot.
Do you have the OS X firewall enabled?

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

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