I have The One Plan from 3. I use my iPhone 4S as a modem for my MacBook as it supports tethering but I am very suspicious that someone in my street is using my Internet connection. I just received my first bill and according to 3 I have use nearly 1GB data in the past 10 days. However I have only watched about four 5 minute videos off YouTube and downloaded a file that's only 50mb. All the rest is just general browsing of websites like forums and news sites. I use the Personal Hotspot function on my iPhone which is passport protected whenever I want to use my iPhone as a modem. However, I am suspicious that someone in my street is hacking into my iPhone and using the net. Please advise.