Security Experts:

Sophos Products Detect Legitimate Windows File as Malware

Sophos rushed to release an update over the weekend after system administrators started complaining that the security firm’s products had flagged a legitimate Windows file as malicious.

Users of Sophos Home, UTM, Central and Enterprise Console products were notified that the Troj/FarFli-CT malware was detected in C:\Windows\System32\winlogon.exe, a component of the Windows login system.

Winlogon.exe is known to be abused by malware, but an error in one of Sophos’ endpoint protection verification systems caused products to detect the file as a threat even without the presence of an infection, leading to blue or black screens in some cases.

According to Sophos, the false positive affected a specific 32-bit version of Windows 7 SP1. The vendor said it had released a fix within hours after learning about the problem.

“Based on current case volume and customer feedback, we believe the number of impacted systems to be minimal and confined to a small number of cases,” Sophos said. “The most common impact to our customer base is that some administrators may need to clear several erroneous alerts from their administrator consoles.”

After the fix is applied, affected users might have to clear the false positive alerts in their product’s console.

Some affected customers took their frustration to Twitter where they complained about the impact of this incident and the long waiting times for reaching the security firm’s tech support.

Problematic false positives and updates are not uncommon. In the past years, such issues hit companies such as Microsoft, Panda Security and Norton. In one of the more recent incidents, an update released by ESET for home and business products prevented users from accessing many popular websites, including eBay, Amazon and Google.

A study conducted last year by Damballa showed that erroneous malware alerts cost organizations roughly $1.3 million per year.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.