Yahoo(NASDAQ: YHOO) has decided to stop allowing customers to access its services, including the Flickr photo-sharing platform, by using Facebook (META -12.33%) or Google (GOOGL -2.56%) log-in credentials. Instead the company will require anyone who wants to use products like its suite of fantasy sports games to create a Yahoo ID.

"Yahoo is continually working on improving the user experience," the company said in a statement Reuters reported, noting that the new process "will allow us to offer the best personalized experience to everyone."

The new forced Yahoo log-in is already in place on the company's College Basketball Tourney Pick'em game, which is tied to the upcoming NCAA men's basketball tournament. On that site the Facebook and Google account log-in buttons are still there. But after customers enter their log-in, they are brought to a page that says "The Google ID you entered is not associated with a Yahoo account. To continue, you now need to create a Yahoo account."

Yahoo owns a lot of content

One of the key tasks facing relatively new Yahoo! CEO Marissa Mayer is reinvigorating the company's advertising base. Part of her strategy has been refreshing a number of products including Yahoo Mail and Yahoo Finance. She has also led an overhaul of a number of apps, launched content sites covering technology and food, and hired Katie Couric as lead news anchor.

Not all of those content platforms require a log-in but most offer services that do.

Tumblr users may not be happy with Yahoo

Under Mayer Yahoo also bought Tumblr, whose change-resistant user base might not react well to the log-in change. Tumblr currently has its own proprietary log-in and Yahoo has not commented on whether it will require the brand -- which it owns but runs separately -- to make the change.

When it announced the acquisition, Yahoo's press release was headlined, "Yahoo to acquire Tumblr" with the tongue-in-cheek subhead, "Promises not to screw it up." 

"Tumblr will be independently operated as a separate business. David Karp will remain CEO. The product, service, and brand will continue to be defined and developed separately with the same Tumblr irreverence, wit, and commitment to empower creators," said the press release.

And while a changed log-in wouldn't amount to "screwing it up," it could be seen that way by the site's hundreds of millions of monthly users.

Yahoo's move makes sense, but it's a risk

In eliminating a log-in method that shares data with competitors and installing one that creates proprietary data, Yahoo is working to improve its ability to deliver targeted ads. There is an inherent risk, however, that customers simply won't want to create a new log-in and will flee for services where they already have credentials.

Google and Facebook log-ins are a customer convenience. They let people access all sorts of sites without having to remember new passwords and user names. Convenience matters and some customers simply won't bother creating a new account with Yahoo just to play a fantasy basketball game (especially if they can play one someplace they already have an account).

"The world is increasingly moving to a model where one identity works across a plethora of disparate solutions – this decision is several steps backwards and does nothing to make Yahoo look like it's learning anything from all those cool start-ups they keep acquiring," Ben Kepes wrote on Fortune.com.

Encouraging customers to create a Yahoo ID and even providing incentives for them to do so makes sense. Forcing them to do it is a bad idea that could backfire and send some users away from Yahoo's sites -- at least those that require log-in. As much as Yahoo wants to collect its own data -- which is a good idea -- it should not prioritize that over the convenience of its customers.

Yahoo would do well to remember that the Internet is not a store that customers invested time and effort in visiting. Instead -- with the next store just a click away -- minor missteps in customer service can have huge negative results. (Think Apple's (AAPL -0.24%) misstep and apology over not including Google Maps in its 2012 iOS update). Making doing business with you harder for your customers is always a bad idea and Mayer should consider dropping this strategy before she scares too many people away.