What are these strange embedded link advertisements on web pages that shouldn’t have such content?

Question

^{My question might seem similar to “How to Block Static Ads”, however I am asking for the server-side prevention, rather than the client-side prevention.}

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This is something I have been seeing over a long time, so I cannot think of a specific example now but sometimes, when I visit a webpage, I notice that about 30% of the text is highlighted blue. If it is a download page, then words like free or download are also highlighted. Upon clicking them, I get brought to some absolutely irrelevant webpage. When I hover over the text, I see some irrelevant advertisement with something like powered by infolinks.

What are these strange ads? How did they put the ads on the page? I have tried cheap hosting rather than hosting pages myself, and I found it to be overrun by advertisements in no time. Is this the same?

Answer 1

The problem you describe is sometimes due to adware on the system which is being used to browse the web, which will inject ads into the pages displayed. Sometimes the adware will monitor someone's browsing habits to display "targeted" ads.

Some applications that have free editions which can be used to check a system for adware/spyware include the following:

Ad-aware

Malwarebytes Anti-Malware

Spybot Search & Destroy

SUPERAntispyware

Assuming, however, that there is no adware on the client side, but, instead, the ads are being served by the website you are visiting, then what you are seeing may be the result of the website owner having an "affiliate" relationship with some advertising network to get revenue from the website, since ads are the mechanism used by most sites to sustain operation of the sites. Here is some information from the Wikipedia article on Infolinks:

Infolinks is an online advertising platform which offers advertising products for publishers, advertisers and brands. The company's products, including InFrame, InSearch, InTag and InText, were designed to overcome banner blindness. Infolinks In3 (Infolinks Intent Intelligence) platform analyzes text on websites and inserts adverts in the text.

The highlighted words may be "in-text advertising" and the website may be using JavaScript provided by the advertising platform or some other mechanism to alter how the page is displayed to your browser to include the ad links when you visit the site.

Answer 2

As other posters have intimated, this is not a problem which can easily be fixed server side - rather the browser has been compromised to modify the text.

Thinking outside the square, it may be possible to write some code to compare the html you sent with what the browser rendered (ie using javascript) and pop up a note if a compromise is detected.