My modem is connected to 4 PCs on LAN. I notice that one of the PCs is causing the internet to slow down when connected.

Let's call it PC 1. When PC 1 is not connected to the modem, only the other three PC 2-4 connected, I run a speedtest and can GET around 4Mbps. But once PC 1 is connnected, the speed will DROP drastically to around 2.5Mbps. Tested a few times and ALSO tried to swap PC 1 to other ports, same result.

The PC 1 is not downloading or streaming anything at the time of testing.

What could be the reason for the bandwidth drainage?What do you think?
A. Bad Hardware?
-or-
B. Bad Software?

A bad NIC (Network Interface Card) can cause errors to  force the system to retry several times when pockets are lost.
This is an easy fix. Buy a new NIC.

Bad Software could be some Malware using the PC1 to spawn attacks on other systems. Or using it for torrent files. Finding it can be hard.
Look at this:
http://forums.majorgeeks.com/showthread.php?t=215493
Bandwith stealing malware


Hi Geek,

I thought of the two possibilities too.
Anyway, the owner of that PC is not around now. I'll talk to him to check for the possible issue when he is back.

Thanks.Hi Geek,

It turns out that he is leaving an online game running at the background even though he is not playing it.
Probably the game is sending/receiving information to/from the the game server even in idle mode.

Thanks.


That makes sense. Some on line games you can lose you R place if you log out. And some users have 'cheat' scripts that keep thyme in the game and they get fame.

Can  he get his own internet connection?

Hi Geek,

He left it running at background so that he does not have to load the game again when he WANTS to play, not because of the game progress. He was not aware that by doing so the game would drain the bandwidth.

Anyway, now he knows it and will close the game when he is not playing.