(AP Photo/Karly Domb Sadof)

After a week of controversy, Instagram is unblocking the #curvy hashtag, effective Thursday afternoon.

Instagram first prevented users from searching for photos with the term last week, prompting a huge backlash from users and women's advocacy groups who were outraged to see a term normally associated with body-positive messages removed from the site. A spate of replacement hashtags, including "curvee," "bringcurvyback" sprang up to fill in the gap.

The problem was that the #curvy hashtag was being used for other reasons, said Nicky Jackson Colaco, Instagram's director of public policy. Namely, pornography.

And the tag was overrun, she said. Instagram has protocols in place to flag when any term is being consistently associated with content that breaks the company's terms of service. Jackson Colaco said that Instagram removes several tags every day when analysis from the company's automated and human content filtering systems get reports from users that they've become a problem. And at some point last week, #curvy hit the tipping point.

The decision to block #curvy, therefore, really had nothing to do with its meaning at all. "This wasn't curvy pornography, this was just irrelevant pornography" that used the hashtag, Jackson Colaco said.

The fact that the term "curvy" has such meaning itself may have even contributed to the fact that it was blocked. Many critics of Instagram have noted that tags with sexually explicit meanings have not been blocked; Colaco Jackson said that could be because the people looking for those terms aren't likely to report an issue when they find their search turns up pornography. Reports tend to come in when people are looking up terms they don't know are associated with porn and are surprised by the images they see.

But, she added, the company certainly understands how important the term is to the people who use to express a positive body image.  So as Instagram moves to restore the hashtag, it's also taken the time to find new tools to help it better parse through the photos that its 300 million users post to the site every day.

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That means stepping up curation of the hashtag, particularly on sections of the service that highlight the "top posts" and "most recent" posts using the marker to make sure that no one looking at #curvy pictures gets an obscene surprise.

"There is nobody who’s cherry-picking terms [to ban]," she said. "And the silver lining in this we have been made aware of terms that hadn’t gotten reported. We're trying to be as consistent as possible."

Colaco Jackson said that the recent controversy was particularly hard for Instagram to deal with because it's tried hard to highlight body-positive messages in the past, going so far as to place interstitial warnings on searches for hashtags that promote eating disorders such as #mia #ana and #thinspiration. The warning also offers up a link to Instagram's health center, where people can find out more about the danger of eating disorders.

"We try to be really thoughtful about looking at these issues," Colaco Jackson said. "There is zero chance" that the company would intentionally try to stifle the positive messages that people who use the #curvy hashtag were communicating, she said.

Apart from this particular case, however, the #curvy controversy does highlight a major problem for Instagram and other social networks that give their users free rein to express themselves. This incident shows that hashtags can be hijacked, for example, and that these services have imperfect tools in place to deal with issues as they come up.

Colaco Jackson said that, over the long-term, Instagram will consider more heavily curating its "top posts" and "most recent" sections of searches, perhaps in some cases removing the real-time feed so that people searching for apparently innocuous search terms don't get an obscene surprise. Meanwhile, the company will continue to develop photo recognition and filtering software over time to hopefully allow it to properly balance safety and expression.

"We won’t be perfect," Colaco Jackson said. "but we will be thoughtful."