Social networks provide a ripe ground for advertising, and somehow Twitter has managed to avoid tailored ads for some time now. That appears to be changing in the future, as cookie-based ad delivery will soon be tested on Twitter.
The new tailored ads will be initially tested in the U.S.; if successful, they could expand to other markets. In all probability, this type of advertising will be more profitable for the company, though it's controversial all the same, as similar tactics have raised concerns about privacy in the past.
Rather remarkably, the service also details how to avoid becoming a target for tailored ads. This can be done within a user's Twitter privacy settings, where 'Promoted Content' can be disabled. In addition, the site will allow "Do Not Track" features to really help prevent ad tailoring.
In a way, you could say Twitter already tailors ads. Within the mobile clients at least, the promoted tweets are often highlighted as being followed by someone you follow. While this may be the case, the company clearly seems to know where it's taking advertisers next.