Screenshots show how a link to moneysupermarket.com was placed under visible links in the "Partner Sites" section of pages at the FT. Hidden links like this are something search engines such as Google warn against doing, lest they be considered search spam.
An update to the story provides some comments from the FT, saying it had a relationship with moneysupermarket.com and that the links had been made visible (I didn't see any links when I looked today, visible or hidden).
Interestingly, the FT had no comment about why the links were hidden originally. That reminds me of WordPress, where hidden links that service was found to have earlier this year lead to search spam. While admitting they were wrong, why they were hidden in the first place was never answered.
Newspapers selling links isn't new. Stanford Daily Removes Paid Links from our blog last month looks at how the student paper at Stanford University recently removed paid listings after coming under fire again that they were being sold in a way that worked against search relevancy.
Stanford University's Student Paper & Selling Links for Search Engine Watch members in April looked at the issue in depth, and how other student papers not to mention major media outlets like the Washington Post and CBS News also sell links. Our forum thread Stanford Daily Selling Links also has discussion on the issue.
In none of these cases, however, were the links hidden from view. People can and sell links for any reasons they want and in fact have been doing so since before search engines depended on them heavily to rank pages.
A search engine might view off-topic links at at attempt to spam them and perhaps even penalize the site and those involved, as happened with SearchKing. Then again, it might not. Was the main reason the link was sold to try and influence search rankings? If so, then they'd be more likely to consider that an attempt to spam them. A hidden paid link pretty much has only one reason to be hidden -- to influence search engines.Postscript: The New York Times has a short brief on the story with a quote from the FT on not wanting to clog its page "real estate" with an "overt link."