I'm not even sure how to refer to this succinctly enough to search the problem on these forums.  Our DATA plan allows 150 gigs of data downloaded per MONTH, with 50 gig automatically added for $10 when that amount's exceeded.  We've been using this plan with no problem for years, but suddenly (like in the last two-three weeks) we're showing days of 25-35 gig downloads.  (We don't stream movies or music, we have only the two home computers connected to the internet by LAN cables).  We thought that maybe someone in the neighborhood had gotten a free ride on our wireless, so we turned that off, and also changed the key and password.  That helped for about 4 days, and then the big downloads showed up again.  AT&T agree that our history doesn't match current usage, was helpful in getting to the Netgear page to turn off wireless, but otherwise not taking much of an interest in this weirdness.  It seems to me a useful, though excessive, step to turn the router off completely when we're not using it, but mainly I have two questions:  1. will it harm the router or computer to just unplug the router and plug it BACK in when we need it? and 2. does this sound to anyone else like one of our computers has some malicious use being run REMOTELY despite Kasperski anti-virus and Ad-aware scans being run daily?

Any thoughts would be hugely welcome.  The computer I'm working on is an ASUS CG5270 quad core 8 GB 64 bit.  Windows is VISTA Home, Service Pack 2.  Video card is Nvidea GeForce GT 220, which Blizzard tells me is no longer useful for Warcraft.  The other computer is an A-open running XP, not sure of the details, but can get them.Any thought? Well you have to talk to AT&T technical support.
The number used in USA is 1-800-288-2020 open 24/7.

If AT&T can not help you, cancel your plan and report the incident to the agency that handles telecommunications regulations in your area.

FCC in USA
http://www.fcc.gov/

In Canada find:
Canadian Radio-television Telecommunications Commission

In California:
California Public Utilities Commission
http://www.cpuc.ca.gov/puc/

My guess is somebody is tanking your bandwidth by some kind of thing that is very illegal to have and use.

Here is one of many things I found:
Tethering a Kindle for free 3G - Hack a Day
Of course I am not giving the link.
Just  want to give everybody a heads up.

When one gets 'free' data, somebody else pays for it. 
Oh, you got the laugh by suggesting we talk to AT&T.  I really appreciate the information you posted regarding contacting interested parties, and the advice to report to the FCC is one we hadn't considered.  AT&T has been called .  We've talked to at least 10 different people, over the course of several days, sometimes for hours, no luck so far.

Thank you for your interest, though.Believe it. AT&T and others are under current investigations.
This just in...
http://www.phonearena.com/news/Are-AT-T-and-T-Mobile-overcharging-their-pre-paid-customers_id53922
Are AT&T and T-Mobile overcharging their pre-paid customers?

Another:
http://www.androidheadlines.com/2014/03/t-mobile-att-prepaid-customers-complaining-per-minute-overcharges.html

Last month:
http://www.theinquirer.net/inquirer/news/2328707/fcc-complaint-claims-at-t-is-overcharging-for-calls-to-collect-user-location-data

Awhile back:
AT&T Sued for Overcharging on Data
http://www.mobiledia.com/news/91056.html

So next time you talk to them, tell them  -
"This conversation is being recorded."