What did you have for breakfast last Friday? No I can't remember either, though my choices are limited to nothing and a banana. What were you watching on tv five fridays ago? What were you searching for on google five fridays ago? What bar did you pop into five fridays ago? What computer game were you playing the following saturday afternoon?
If you know the answer to more than one of those questions, you've got a better memory than I do. More likely you don't but you could probably find out. Check the last Tesco online delivery for what cereal you bought. Sign in to netflix and check your history for the name of that tv programme, a little poking about in your browser history should reveal what you were searching for a few weeks ago, facebook can probably tell you which bar you went to, what you drank, who with and what happened 'afterwards'. Steam can tell you what you were playing that Saturday, and how well you were doing.
Five different pieces of information from five different services which on their own say very little. Put together they become a remarkably detailed snapshot of your life. These are just a few of the numerous things the internet knows about you. How much do you get paid (you do online banking right?). How much of that goes on bills? I bet you pay them online too. Last time you got lost, did you check google maps on your smartphone? Did it finish typing you sentence for you? How did it know you wanted directions to the Shell station in Leamington Spa? And how in the name of Jobs' turtleneck did it know where you were to within three feet?
We all use these services, and it's taken a remarkably short amount of time for them to go from novelty to luxury to basic human right ('Your phone doesn't have satnav? How do you survive?' coo some of my more gadget-o-philic friends). What many people don't realise is these services record everything. Google has your search history and probably most of your browsing history, Apple keep a record of everything you say to Siri and can share it with pretty much whoever they want (see section 4c), Facebook have been in hot water about their data retention practices and unless you permanently browse 'incognito', your PC will have a record of everything you've ever done online through it and probably a few things you haven't.
Before I start sounding like a luddite with a penchent for tinfoil hats, let me say I use several of the services mentioned, though not all of them. What makes me nervous is there are half a dozen companies that know more about my life than I do and the fact is that information isn't safe. Sony/PSN, LinkedIn, Apple, Blizzard and even RSA have all been compromised wholesale. The latter is a security company, clients of whom include financial institutions and defence contractors. If money and weapons can't be kept safe, what hope is there for a few blurry photos? If you're unlucky enough to be targeted individually you'll probably end up feeling like Mat Honan. If an organisation that holds your data is compromised, the information will probably be sold to the highest bidder.
Scared? You probably should be. Is there anything you can do about it? You can take some precations. Have a look at Tom's post about passwords and how not to form them. Use different ones for each service, or at least intelligent variatons on a theme. Lock down your facebook profile so that only friends can see it. Browse in 'privacy mode' (or whichever flavour is present in your browser). If you can't bear to do that, clear your history and cache every so often.
These are just good habits to get into. It's like locking your door and closing your curtains at night or putting timer switches on your lamps when you go on holiday. Oh and please, whatever you do, don't do this.