The online photo-sharing service Flickr shared more photographs than it was supposed to.

Flickr, which is owned by Yahoo, emailed some users this past weekend to warn them that some of their photos marked "private" were instead made publicly available: "While performing routine site maintenance, we identified a software bug that may have changed the view setting on some of your photos from non-public (i.e., private or viewable only by family and friends) to public," according to the Flickr email, which was signed by Flickr VP Brett Wayn. "The affected photos were visible on Flickr between January 18th and February 7th, 2013."

"We're deeply sorry this happened," said Wayn. "We've put in place a number of additional measures to prevent this from happening again."

The bug affected some images uploaded between April and December 2012. "Overall, this issue impacted only a small percentage of photos," according to Wayn's email. On average, however, 1.4 million photos marked "public" were uploaded to Flickr daily in 2012, meaning that tens of millions of private photos could have been made public.

[ Third-party integration is convenient, but it can be risky, too. See Facebook Login Bug: Lessons Learned. ]

Yahoo didn't immediately respond to emailed questions about how many Flickr users were affected, how many images were exposed or whether Yahoo has finished contacting all affected users by email. In addition, "Flickr was unable to tell me if anyone actually did see my private photos, when I asked," reported paid Flickr account holder Barry Schwartz, who's the CEO of RustyBrick and news editor of Search Engine Land, and who received a "Dear Barry" letter from Flickr.

Flickr's email noted that none of the affected images were displayed by Flickr's own search engine or allowed to be indexed by third-party search engines. But the affected images would have been viewable when visiting an affected user's Flickr "photostream," or browsing to the image via a link.

As a precautionary measure, Flickr set the "who can see this photo?" settings for any potentially affected image to "private." But that blanket change means any public images that were embedded in third-party websites, or linked to from other websites, now display a broken link. Multiple affected users have taken to the Flickr help forum to complain that they have to manually review all of their images to try and spot the ones that are now marked as private, but which should really be public.

Flickr recently appeared to get a new lease on life after Google product development VP Marissa Mayer last year assumed the helm of Yahoo, and pushed Yahoo product upgrades, including a revamped mobile Flickr app.

But this isn't the only recently discovered Yahoo privacy or data security snafu. The company was already in the news this week after information security journalist Brian Krebs reported Monday that Yahoo's free, consumer-focused website building tool, SiteBuilder, which runs on Windows, bundles a "dangerously insecure" version of Java that dates from summer 2008.

The most recent version of Java 6 is update 39, which includes fixes for numerous vulnerabilities in older Java 6 versions that are actively targeted by attackers, oftentimes via automated crimeware toolkits. For comparison's sake, the version of Java bundled with SiteBuilder is Java 6 Update 7, which was released more than four years ago. As a result, anyone who uses SiteBuilder but fails to update the included Java software is putting their PC at risk of being compromised.