I have experienced a simple version of web monitoring myself: since simply checking out some office chairs at some obscure shopping website, almost every website I visit (including my own blog) is plastered with multiple Google Ads of that specific shop. After several weeks, the office chair issue is long vanished, but the ads still persist. Where can I opt out please?

[wsj.com] is an interactive graph by the Wall Street Journal, illustrating the degree to which the 50 most popular websites exposes visitors to monitoring (think cookies, beacons, Flash cookies and the like, which together reveal large parts of your past browsing patterns).

Each red slice at the top represents a unique website, like msn.com or photobucket.com. Each website tends to send hundreds of tracker files to third-party websites, such as Google, AOL, Yahoo, or Microsoft. Figure out yourself why (26 trackers) seems like an angel next to privacy-grabbing websites such as (131 trackers) or (118 trackers).