Microsoft, Third-Party Antivirus Apps Block uTorrent Due to Possible Threat

Windows Defender, the default antivirus solution bundled into Windows 8.1 and Windows 10, as well as several third-party security products have begun blocking BitTorrent client uTorrent due to a possible threat on systems running Microsoft’s desktop operating system.

The application is flagged as Potentially Unwanted Software (also known as Potentially Unwanted Application or PUA) by Windows Defender, ESET’s NOD32, Sophos antivirus engine, and a few others. Kaspersky, Bitdefender, Avast, and F-Secure all claim uTorrent is clean.

At this point, it’s not yet known what’s triggering the block, but it’s believed the built-in modules, like the Web Companion, might be the culprit, despite parent company BitTorrent describing these security warnings as false positives.

While the one to blame for this warning could be the software bundled with uTorrent, BitTorrent says the issue only affects one out of three installers hosted on its website, which is regularly served to just 5 percent of the users. This means a small number of systems got the warning, which in its turn is believed to be pushed by an update that Microsoft released on Patch Tuesday.

“We believe that this passive flag changed to active just hours ago with the Windows patch Tuesday update, when a small percent of users started getting an explicit block,” BitTorrent explained in a statement for TorrentFreak.

“We had three uTorrent executables being served from our site. Two were going to 95% of our users and were not part of the Windows block. The third, which was going to 5% of users, was part of the Windows block. We stopped shipping that and confirmed we are no longer seeing any blocks.”

There are several questions that remained unanswered even after BitTorrent’s statement. For example, while it’d make sense for new installs to be blocked following a patch released by Microsoft this week, it looks like the same warning is also shown in the case of systems already running uTorrent, and the cited source speculates this could be the result of an automatic update.

At the same time, blaming modules that are bundled into the installer, like Lavasoft’s Ad-Aware Web Companion, doesn’t seem to make much sense at first, as Microsoft lists Lavasoft as a verified publisher and thus its software is whitelisted on Windows.

BitTorrent says its installers are fully clean and there’s nothing wrong with uTorrent, and the company continues working with the other firms, including Microsoft and antivirus vendors, to address the alleged false positives.