Mysterious downloading causing satellite internet to go over limit

Question

Sorry for the long post. I have tried a lot of ways to answer my question, or fix my problem.
II have a 3 year old Intel Mac, still working great. Where we live our only high speed option is satellite, so we subscribe to hughesnet. Our downloads are limited to 375 meg per day.
We don't have a real problem staying under, but when it locks ups to 14.4 kbs, we know we have gone over. I eventually installed a few programs to let me know if it was my kids downloading stuff and not telling me, or something else. I installed two download monitoring programs, and Spector for Mac.
In the last month, there have been two incidents where massive downloading caused us to go over the daily limit. Hughesnet has at times locked us out claiming we went over - the download monitors were installed to verify this, and proved otherwise.
However, these last two times, the download monitors verified a download of over 300 meg within the space of an hour, part of the time while I was on the computer.
I have tried every way in the world to discover what the culprit was, what the files were, but I cannot.
I have checked the download records and histories of all three browsers, and these show nothing. Spector verified almost no browser use during the time in question.
I checked Itunes to see if anything, whether music, movies or podcasts had been added during that time frame. Nothing.
I checked the date of files in the download folder, both "created" and "modified". Nothing there.
I check the software updater(This had been a problem in the past). The log of downloaded updates shows no activity there as well.
My e-mail program didn't show any automatic downloads with massive file attachments, either.
It left me scratching my head.
After this happened a few weeks ago, I downloaded a 30-day trial of Intego Internet Security Barrier X6. Virus program, firewall, and a couple of other programs, I updated it and did a virus/trojan scan on my computer, with no results. I was completely clean. The antivirus program really slowed down the Mac, of course, and it got so bad that after a few days i couldn't take any more, so I uninstalled it.
The only options I haven't tried yet are scanning the backup drive( assumed this was scanned at the same time when I scanned the main nard drive, but am not sure) and possible a couple of other partitions. I have Windows XP installed on this computer through bootcamp, but haven't booted up in over 2 months. I also have a second version of windows installed within the mac osx partition through a Virtualbox program. I don't know if a virus could be hiding in there, but I am relatively certain that I installed antivirus protection on it and updated it as well. Even at that, I don't know if a trojan or virus could be play havoc while the program is turned off.
That is what I have done so far, and am out of ideas. Does anyone know of a way I can track down what this was?
If not, does anyone know of a program that could monitor this in the future and alert me to massive unauthorized downloads?
All comments and ideas are appreciated.
Fred

Answer 1

There may be a way to monitor who (else) may have access, presumably
unauthorized and more possible if you have a local wireless aspect to your
home or business network where someone else not so far away could get in.
As both up and down load activities can be monitored, are you able to tell if
some of your usage is due to something in the computers "calling out" online
and them perhaps something else connecting back to your computers? The
app Little Snitch will tell what may be attempting some connections out.
Sometimes, you can tell if another computer is on a local network, unless that
owner or user has somehow set their computer to be invisible to a network it
may be borrowing internet access from.
Do you have any apps that offer an option to provide backups online to some
outside server? Some kinds of products can offer web-dependent services.
Even widgets in DashBoard can consume bandwidth. I have and use a widget
that turns off all widgets until I launch DashBoard. Dash-quit is a handy tool.
{Having dual operating systems in the computers, possibly could be an issue;
but whether or not your configurations are accessing the internet somehow,
is an unknown to me. If the Windows systems can't go online while you aren't
using them, maybe those aren't a probable cause of this; until they actually are.}
Is the network usage statistic based on mbps, kbps or some other set of numbers
where your version may appear different than that of the provider? Some of the
math (like MB vs. GB in drive capacities; comparing grapes and bananas) can be
harder to follow if one entity derives their quota from a different connection math.
Almost as bad in a few cases, as the cited hard disk drive capacities, when there
may be two different kinds of numbers!
I've only used dialup, ADSL, and some low-end cable internet. Had dish TV but
at the time, they offered nothing for internet; except weather outages of all signal.
If you have nothing checking for automatic updates, including apps that may offer it;
and have the firewall set to not allow some invasive efforts of outside connections
to try and hook up to your network, and no body accessing your satellite internet via
a wireless component whose security is not what it should be; I am not so sure what
kind of other thing you'd need to be looking into at this point. Apparently something.
Good luck & happy computing!