Want to know who's spying on you online? There's an app for that

Summary: Mozilla has released a tool that will allow users of the Firefox browser to know which companies are tracking them online.

Would you like to know who's watching what websites you visit? Well there's an app for that.

It's standard practice for advertisers to keeps tabs on the sites you frequent using tracking cookies. Tracking cookies are small text files that are downloaded on to your computer that log the websites you browse and, in some case, how you interact with these sites. Advertisers and other companies use these logs to build a profile of your interests, allowing advertisers to sell you products and services you're more likely to buy.

In an attempt to highlight just how many different firms are tracking our browsing habits online Mozilla has produced Lightbeam, an add-on that can be downloaded for the Firefox browser that captures who is watching you.

Every time you visit a site the tool logs every web address that is connecting to your machine, revealing how visiting a single website can result in your computer to connecting to many different web servers. Each of these servers may be controlled by different companies, and send and collect different information, for example serving up images and adverts on the site or placing tracking cookies on your computer.

Each circle shows a web address of a site visited and each triangle a third party site that has connected to your computer. Image: Mozilla

The log is rendered as an infographic that makes it clear which third parties are operating behind the scenes on each website you visit. Users can choose to watch or block individual sites from the tool.

Mozilla's executive director Mark Surman said Lightbeam is about raising public awareness of how their activity is tracked online.

'It really is a stake in the ground designed to start a conversation about privacy,' he said.

'If you think about nutrition it's taken years of policy and public education about different types of food for people to be talk about a healthy diet. This is the same thing, this is saying 'Let's know a little bit more about what's happening' then we can get to discussions about what else is being tracked, to building tools to let you protect yourself, to education campaigns about how what we want to protect about ourselves.'

Information collected by Lightbeam can be uploaded to an online database that aggregates anonymised data about third party tracking across different sites.

'We need people to know how the web works and one element of that is privacy,'said Surman.

'We're figuring out a significant part of how humans interact with each other and that will last for hundreds of years. As we figure that out there are different forces in play, the normal forces of creativity, commerce and government. It's part of society figuring out what the web should be and our role is to stand up for those core values that the web was built on.'

Lightbeam is the next version of an earlier Firefox add-on called Collusion, which also helped web users monitor online tracking.

Mozilla pointed out that tracking cookies are only one of a number of methods that can be used for tracking web users online. Another common approach is for the website you are visiting choosing to share data on who is visiting the site with third parties. Mozilla said that some companies are now using browser fingerprinting, where a user is tracked via the unique way their web browser is set up, for instance in the font sizes selected or the mix of add-ons installed.

Firefox also allows users to select a 'Do not track' option, which sends a message to web servers not to place tracking cookies on a user's computer, however it is up to third parties to comply with these wishes. About 18 per cent of Firefox users in the UK and US use 'Do not track' options.