Outlook bombards Safari users with endless downloads

Mystery zero-byte file deluge makes site unusable, hundreds of netizens complain

Updated Attention, Mac users who access Outlook with Safari: something's broken, and it's causing an empty TokenFactoryIFrame file to be downloaded every few seconds for as long as you remain there.

Microsoft hasn't said what's causing the problem, though it did acknowledge the ongoing blunder in this support message-board thread on Microsoft Answers. We understand this flood of downloads affects Safari on desktop Macs; it may also affect browsers on iOS using Safari's WebKit engine, such as Microsoft Edge on iPads.

The Redmond giant noted in a post dated May 3, "We have recently received several reports that customers have the issue when they visit Outlook in a Safari browser on Mac it keeps downloading token factory iframe. We are doing research on our side to see if we can find any relevant information about the issue." Microsoft has not responded to questions from The Register.

It seems the problem kicked off on May 2, with multiple users posting to Microsoft's help forums to complain about the issue. It appears widespread, too: this support board thread about the downloads has been viewed more than 100,000 times, has had hundreds of replies, and suggests that as of today, the bug is still present. Users on Apple's help forums have also reported the problem.

Günter Born, an engineer and community moderator for Microsoft Answers in Germany, compiled netizens' complaints into a blog post, where he said that it appears the issue is a Microsoft one. "I've linked this article within my post in Microsoft Answers forum and asked the forum moderators to forward the issue to the responsible Microsoft product group – that's all I can do," Born said. 

According to comments Born collected, the bug appears to only happen when Safari users point their browser at Office 365's Outlook Web Access. One user who investigated the issue said that they noticed in the Safari developer console a "failed to load resource" error with a code of 400 (bad request) that pointed to a TokenFactoryIFrame. Multiple reports indicate the bug is happening in the most recent version of Safari (15.4), and multiple versions of macOS.

Several websites have sprung up reporting to offer a solution to the "TokenFactoryIFrame Mac virus," but there's no indication the file contains malware. Multiple posters in the Microsoft Answers thread have said the file is zero bytes in length.

Until Microsoft determines the cause of the problem and deploys a fix on its end, it's possible to enact a workaround by setting Outlook365's download preferences in Safari to deny, though note that this will prevent all downloads from Outlook until it's toggled back. 

Alternatively, use a different browser to access Outlook Web Access, or use the Outlook app, or the bundled Mail app for macOS. ®

Updated to add

It appears that the bug was a server-side error in Microsoft's realm. The company reported in the bug thread that the issue has been resolved and that it confirmed to customers that OWA was back in working order.

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