By Darren Waters
Technology editor, BBC News website
The search engines that power our journey through the internet know a lot about us - from the operating system and browser we use, to the kinds of websites we typically visit.
Google informs me of the sites I have visited most in the last week
As Google comes under scrutiny over its privacy policies in Europe, our technology editor looks at the information that search engines and web services firms record about us.
The websites I visit most frequently include the BBC News website, Wikipedia, Microsoft, Apple and Cnet, while Pirate Bay, the World Time Clock and RFID and wi-fi are among my most searched for terms in the last 30 days.
I know this because Google tells me so. As a Google account holder, and because I asked it to, the computer giant records how I use the internet whenever I am logged into its service.
The data is quite detailed: it shows that I do most of my search engine queries between 11am and noon, but also that I am still busy online through most evenings.
It tells me the products I have searched for, the news items, the video clips, the images and even the maps I have looked at.
If anyone were to look at this information, they would have a comprehensive idea of my lifestyle, my interests and potentially even my movements - Google records that I searched for the location of a hairdressers in Richmond last week.
Yahoo and Microsoft's MSN probably know a lot about me too. I am frequently logged into their services, and while I don't use their search engines, both firms know some personal details because I had to provide them when I registered.
And this is what worries some privacy experts. They want to ensure that this information remains private and is not abused in any way.
The simplest method used by websites to track behaviour is a cookie. These small files are stored on your computer each time you use the net and note the details of the computer that accesses a web page.
Each cookie contain an anonymous unique identifier related to the computer you are using.
Why do firms like Yahoo and Google collect this information?
At the simplest level, the firms track our web usage so they can optimise our experience in the future.
Cookies store preferences, such as language settings, and can also tell websites the preceding website we were looking at and site we go to next.
These files can be switched off in a browser but that does mean that many web services will fail to work properly or will not work at all.
Yahoo, Google and Microsoft also use web beacons, a tiny electronic image on a web page, which helps them analyse a user's behaviour online.
These firms make money online by targeting advertising to users when a search is performed or alongside their web products.
For advertisers, the attraction of the online space is being able to talk directly to customers whom they know are interested in their products or product area.
But who else gets to see or use this personal information? Is my web history, or information about which adverts I look at, being handed over to third parties?
Peter Fleischer, Google's global privacy counsel, says: "No third parties are given access to a Google's user's web history.
According to Google, May is a very popular month for my searches
"We will never transfer to third parties, including advertisers, any personally identifiable information about our users - that includes IP addresses and account details."
Yahoo and MSN's privacy policies also say they do not disclose personal information to third parties without user consent.
Search engines are able to serve up targeted adverts to users not because they know who each user is by name, but because search engines and web services are engineered to interpret what information we are seeking online.
Yahoo combines non-identifiable personal data from account holders, with the web history from using Yahoo websites and services to create a detailed, yet anonymous, profile of a user. That data is then used to serve targeted adverts.
Google does not utilise a user's web surface history to target adverts unless the user has signed up to its personalised web search system.
And it only stores personal information when it has asked a user's opinion.
Mr Fleischer says: "It should always be an opt in if the service proposes to collect sensitive personal information, such as health information.
"If it is doing something routine, then an opt out is fine, such as downloading cookies to a machine."
Mr Fleischer explains: "If you are a user of personalised search - which is an opt-in service - we could take into account your web browsing history from the past to provide more relevant search results.
"The advertisers would be bidding against those more relevant search results."
So does it matter if that information about us is anonymised?
Mr Fleischer believes that it is inevitable that more and more data will exist about us in cyberspace but does not think that will mean our right to privacy is compromised.
"More and more of these services will offer choice about how to use them.
"I am speculating here, but I would expect that people will be able to say how they want to use services, whether in an identifiable capacity or under a pseudonym.
"There are all kinds of different levels of transparency you can choose to represent different parts of your lives. Over time people will become much more sophisticated about how they use all this online data about themselves."
He adds: "We are in a transition generation right now. As individuals and society we need to learn new ways to deal with wanting to be identifiable, wanting to be anonymous and if we want to be pseudonymous.
"Technology companies will build tools for people to do this. It will become a very natural part of our lives within five years."