These are attempts at underhanded betrayal of trust.
Yahoo! & Google breach of trust to it's patrons reached a new low.
Both services submissively bowed to advertising conglomerates, by adopting 'phorm' inspired "targeted advertising"; a 'data siphon' method that directs your clickstream to advertisers, and builds a portfolio on your surf habits.
This may make your browser display pop-ups which you have no control over, and may in fact do many other un-requested actions with your entire system.
Google itself has spyware.
From their Privacy Center page
(http://www.google.com/privacy_ads.html)
"No personally identifiable information – We don’t collect or serve ads based on personal information without your permission."
Notice the last 3 words...yet it is specifically an "Opt Out" condition!
And Gmail, once perceived to be 'safe', actually scans all your mail & then selects advertising based on the content. It's "for your own good...."
http://mail.google.com/mail/help/about_privacy.html
"Google uses the DoubleClick DART cookie on our Google content network ..."
Opt out of DoubleClick here:
http://www.doubleclick.com/privacy/dart_adserving.aspx
These guys are the used car salesman of the internet, very 'slippery' characters burying their methods, details & opt out choices with layer after layer, page after page of non-sense & merry-go-round tactics plus non-functioning links, etc.
All I can say is keep trying & get as many of these tracking portfolios killed as you can.
Yahoo! calls their invasion of privacy "Matched advertising", and it stems from the 'Network Advertising Initiative' (NAI), a conglomerate of advertising kingpins and requires "Opt Out" to defray the advertising tsunami from Yahoo's partners in this server based spyware/adware (and to stop them from creating a 'profile' of you).
"Opt out" sign in pages;
Yahoo here: http://info.yahoo.com/relevantads/
Google here: http://www.google.com/privacy_ads.html
NAI garbage here: http://networkadvertising.org/managing/o...
DoubleClick here: http://www.doubleclick.com/privacy/dart_adserving.aspx
For more detail of this blatant violation of trust, and it's creeping privacy invasion implications, listen to Security Now podcast #153, http://twit.tv/sn153