With deep packet inspection the networks can be quite clever. You never know when they are going to tweak the detection either.

They can see all of the data and headers in the packets traversing the network. If some packets coming from you are not in keeping with a mobile device then they can display a tethering block page. If more and more people keep abusing it and not adding the tethering addon then it's likely the detection measures will become more sophisticated.

Here are some things to think about - these are things they could use to detect tethering, I'm not saying they do, but with deep packet inspection they could.

Does your phone do Windows updates or send packets to check to see if there are new updates available. These are done over HTTP with hardcoded desktop user agent strings.

Not just your browser but any software doing anything that connects to the internet over HTTP will use a user agent string. We've seen instances where Three's detection was being triggered by an android app with the wrong user agent string coded.

Even more advanced and unlikely, but if people continue to try and bypass it they could even look at things like the differences in the TCP protocol window sizes between windows desktop / laptop devices and Android / IOS.

If people are on unlimited phone data you can see why the networks would want them to pay £5 more to add another device on the unlimited data plan, as a desktop or laptop device is likely to use a lot more data than a phone.

I read Giffgaff are going to implement sophisticated anti-tethering techniques on plans that don't allow it. it was in the slide deck that they put out when they talked about the price rises, they did say which quarter they planned to introduce it, but I can't remember when it was, sometime in the next 6 months I think.

Found it, here's the plan that Giffgaff are going to implement over the next few months, it will block tethering automatically when requests come from non phone devices unless you have bought the gigabag and are allowed to tether.

http://image.slidesharecdn.com/whole...jpg?1347291588

It's an immediate 1/2 hour block of all data when it sees non phone requests from when it's implemented, which is in the next few months.

It's a bit hearsay but I have a friend with 3 unlimited data (not one plan, it's like a 2 pound addon). He bought a Windows Phone to try out.

Certain apps and I'm not sure which ones caused 3 to shut his connection down and tell him to stop tethering - except he wasn't.

I assume Windows Phone is so unpopular, 3 haven't rigged their DPI to cope with it

It's all in the user agents and stuff, I used to tether my giffgaff SIM from my android phone to my iphone all the time using GBs and GBs a month and nothing happened, yet one day i tether to my macbook for 5 ins and i get barred.

Windows... Phone...?

Never heard of it... Not one of those cheap Chinese knock off things is it. probably why Three thought he was tethering.

Tbh i think networks need to try and find a balance between blocking everything and blocking the right things.

It probably matched a regex for windows update or something. Like you say it needs tweaking.

If people didn't cheat then the networks wouldn't have to do this stuff.

Really?
I've never heard of anyone getting round the block before - well, not unless they negotiated it as part of their upgrade deal anyway.

There isn't a block (not that I've encountered, anyway). They haven't even disabled the tethering option on my iPhone carrier settings.

I use my iPhone to tether my laptop all the time on 3 and I've never seen a block page nor do I get charged extra for it. Strange.

What's supposed to happen on the updated Full Monty tariffs is that if you try and tether, you're taken to a page and prompted to pay for the tethering in advance.
The rates are the same as their PAYG broadband - £2/day, £7/week, £15/month (IIRC).

Because they offer people the option of paying, they don't remove the tethering options from the settings menu on the iPhone.

My mate has an iPhone 5 on Three's Ultimate Internet 500 and even though that's not a tethering plan he still has the tethering option in the iPhone... Why is that? I thought they would disable it for plans that don't allow it.

IPhones download a "network profile" which can enable or disable WiFi hotspot creation.

This isn't quite "enabling or encouraging" tethering"! The control Apple allow the networks isn't fine enough as some SIMs on some plans (mobile broadband for one!) will be perfectly legal to tether with!

Sure its been said, but just to echo, I found a really reasonable offer the other day, which I signed up with purely as it was such good terms.

Nokia E5 / Ultimate Internet 500 £10
Add Tethering (monthly rolling).£5

I got a slightly aging Nokia E5, lots of minutes, texts etc, and UNLIMITED Internet.!!
What made this great was the 2nd line=>>
"Add £5 for tethering to 5 other devices.'
Regardless what folk say, getting the E5 to act as the mobile hotspot took about 30 seconds and one google search for help.
I have it working on - 2 Laptop/ Net Book PCs at home, IPpad 4 w Retina, Kobo Vox,and a Samsung galaxy unlocked, and thats along with a decent enough handset that I can change and keep the £15 sim for use on any other unlocked phone , you can pick them up for £20+ these days
Thats it, all that for £15 a month. Unlimited, and tethering legally!!, not on the sly hoping they dont find out and block you. From 3, its this months bargain offer.
Hope this helps some folk.

The £5 tethering pack has a 1GB limit