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Phishing Emails Remain in User Inboxes Over 3 Days Before They're Removed

Most malicious emails get blocked, but the ones that get through linger around dangerously long, a new study shows.

Enterprise organizations, on average, take more than three days to discover and remove phishing emails that passed their security defenses and landed in employee inboxes.

Contributing to the delay is a combination of factors, including a lack of investigative tools, security resources, and employee awareness.

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Barracuda Network recently analyzed data gathered from some 3,500 organizations in a bid to better understand what happens after a phishing email ends up on a user system. The analysis shows an average organization with around 1,100 employees experienced around 15 incidents per month where phishing email got past their malware- and email- filtering tools. An average of 10 employees were impacted in each of these incidents.

Mike Flouton, vice president, products at Barracuda, says the attacks that do get through enterprise defenses typically tend to be highly targeted and focused on a small set of selected users within an organization. 

"So it's not the case that 10 users received emails and others didn't because it was blocked, but rather attackers targeted 10 users only to begin with," Flouton says.

Email security tools have generally become very efficient at blocking large-scale attacks, he says. Rather, it's often social engineering attacks that are much smaller in scale that get through.

Phishing continues to be one of the primary attack vectors for threat actors looking for an initial entry point into an enterprise network. Malware hidden in email attachments or on sites to which users are directed after clicking on an email phishing link have caused more compromises in recent years than almost any other attack vector. Verizon's "2021 Data Breach Investigations Report" (DBIR) showed phishing to be the cause for some 36% of the 5,250 breaches that it investigated last year. That number marked a substantial jump from last year's 25% — primarily because of increased phishing activity involving COVD-19 related lures since the pandemic began. 

"Phishing has utilized quarantine to pump up its frequency to being present in 36% of breaches," Verizon said in its report.  

Barracuda's study found 3% of employees who receive a phishing email tend to fall for it by either clicking on a malicious attachment or following a link to a malware-laden site.  Often, such users clicked on a malicious link within 16 minutes after receiving the malicious email.

At the same time, it took IT teams an average of 83 hours, or nearly three-and-a-half days, to discover a malicious email after it landed in a user's email inbox. In most instances — almost 68% — the security team discovered the malicious email through internal threat hunting exercises, including searching through message logs or conducting keyword and sender searches on delivered email. The frequency with which security teams conduct these hunts tends to vary based on an organization's resources. Ideally, it needs to happen daily, Flouton says.

User Training Is Key
Factors that impact an organization's ability to unearth malicious emails faster include a lack of proper tooling, time, resources, and employee awareness.  Barracuda found that when employees report phishing incidents — which is the case with 24% of all incidents — the accuracy of these reports is often low and results in wasted effort for the IT security team.

Properly training employees to identify and report phishing emails can result in faster response times overall. In fact, the accuracy of user-reported incidents can improve up to 73% with just two user awareness training programs, Barracuda said.

"A good formula for security awareness training initiatives is simulate, analyze, educate," Flouton says.

It's a good idea for the security team to simulate a variety of real-world threat types that their organization is likely to experience. For example, users often get tricked into interacting with phishing simulations, such as Office 365 service impersonation and business email compromise.

"By exposing them to these types of attacks and following up with corresponding training material [such as] videos, tip sheets, [and] games, on a consistent basis, users will be more likely to identify social engineering attacks and report them to their IT team," Flouton says.

Other measures that organizations can take to quickly identify and weed out phishing emails from the environment include proactive threat hunting, automation, and tighter integration between incident response and the email and Web security teams, Barracuda said.

Jai Vijayan is a seasoned technology reporter with over 20 years of experience in IT trade journalism. He was most recently a Senior Editor at Computerworld, where he covered information security and data privacy issues for the publication. Over the course of his 20-year ... View Full Bio

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