Ok,Well the good news is its not a trojan or keylogger as...

Ok,

Well the good news is its not a trojan or keylogger as uploads would be a lot higher.
You can also rule out peer to peer software anyway as you would find the upload would be a lot higher also... even if you did limit the upload on peer to peer program it still sends out or uploads packets to retrieve info which would also still should be higher than 10mb if 650mb was downloaded.

Ok... so a couple of things here i need to know about your setup :

1. Do you have a network or wifi setup in the house or does anyone else in the house have laptop or network in another area in the house?

2. I worked in the internet tech support for 10 years and although it is very very very rare you cannot rule out there could be a glitch with the ISP server that keeps track of uploads/downloads. Now i must specify the chances of their servers being wrong is remote by i did encounter this several times over the years but Im talking possibly 3 times over 10 years. You may want to give them a call tomorrow to ask if they can look into your download issue... they might have had an issue themselves and problem solved :)

3. down the bottom right just to the left of the time ( Im assuming your using a PC and not a MAC :) ) you will see a lot of small icons...

i want you to hover your mouse over each and every one of these icons ( and make sure you click the arrow pointing to the right as this will display ALL the icons )to make sure you know exactly what they are and if they are programs that auto update...

these items are in your start up menu so they automatically become active as soon as your computer starts up...

if you dont know what they are jot down the name and then google the name because it may be software that you, your family, your girlfriend or flatmate ( If i had a dollar for each time a found out that someone had secretly installed something on the callers computer that was causing the downloads i would be retired sitting down drinking pina coladas on some beach in the pacific ) has installed or a program that secretly installed along with another program... eg those sneaky add on bars or search bars that come with certain programs )

4. check your email programs... even if you never use outlook express or microsoft outlook or didnt even open them have a look as certain malicious programs can run executable programs to automatically open, setup and download spam or other emails into these programs... if you have third party email programs like thunderbird and have never used them i still want u to open them up and have a look to make sure nothing has been downloade...around 10% of unknown downloads from the calls i received came from emails downloaded into outlook/outlook express even when the customer had never used or set them up...

5.Actually you could probably do this one to start with... do a full scan of your antivirus software and your anti-spyware software... if you dont have any anti-spyware software then first of all... SHAME ON YOU :)... you will need to get one installed... there are quite a number of free ones on the net but... and this should be a big BUT... there are also a number of websites claiming to be anti-spyware but in actual fact install spyware on your computer ( bastards!! ) so best bet is to find someone you know who has already downloaded a properly functioning one and to go to the same website and download...

6. I want u to go to the control panel and open up either add/remove programs if your using Windows XP or "program and features" if your using Vista and as I have never used windows 7 i cannot tell you what the name of it is there but your trying to find the full list of all executable programs you have installed on the machine.
Once you have found the list then i want u to go thru every single one of the items ( ignore anything to do with windows, your antivirus, suncorp systems and any other well known company names like Intel or other items like your printer etc that you know are legitimate programs ) and make sure you know what the program is... i cant stress this enought... make sure u know what every program in here does ...if not sure then google the program to check out what it is...
I can tell you now about 30%-40% of all unknown downloads resulted in me finding some program listed here the user was totally unaware about and causing the issues...

7. try searching your computer for every file that was downloaded today... eg : I have windows vista on all 4 of my machines so for me to do that i do the following
(i) left click on start or the windows "flag" in the bottom left
(ii) in the start search box down the very bottom left ( you should have the flashing cursor automatically flashing in there already ) type in the word "search"
(ii) if you have windows XP you might have to click on the word "find" in the right hand column then click on "files and folders"
(iii) Now there are several different methodologies to try and search for files and or folders based on the date they were modified or created based on the windows version :eg Vista, XP or Windows 7 and as I only have Vista in front of me i cant remember the other methods as its been a several years since I have done tech support so you might have to fiddle your way thru this
(iv) On Vista i have "search everywhere" down the bottom left which i can click on and allows me to search for files that have been created or modified on any date...
(v) if your not sure how to find it you may have to google your version of windows along with the question eg : if you had windows XP you might type into google " how do i search for files/folders that have been modified/created on a certain date in windows XP?"

Anyway... these are only some of the things u can try... let me know how you go... Im actually heading off to bed but will check out the forums tomorrow and depending on your results will give u other items to try... dont forget to advise me about network / wifi / other laptops in house as this may be vitally important...