The rise in email-delivered attacks is a reflection of a pattern that Symantec’s research team calls “living off the land.” It’s essentially a return to basics: Rather than hoarding complex “zero-days”—attacks that exploit security holes for which no patches currently exist—or coding web-based malware, hackers are turning to more straightforward methods.
Macros embedded in Word or Excel documents, for example, saw a surprising comeback in 2016. Macros are mini-programs that automate tedious tasks inside a document, like formatting a table in a certain way, or filling out a long form with personal information. But since they’re designed to execute a series of commands—and aren’t confined to the document they live in—they can be maliciously repurposed. In the late ’90s, a macro virus called Melissa caused $80 million in damage by emailing the first 50 contacts in each victim’s address book.
The popularity of macro viruses plummeted in the early 2000s, when new versions of Microsoft Office came with more restrictive security settings for macros. But in the last few years, they’ve surged again. That’s because attackers have started using social engineering: tricks that convince victims to help the cyberattack along. A Word document with a malicious macro might say, “Please click ‘Enable content’ to view this password-protected document.” When the user does so, the macro is free to do fulfill its destructive instructions.
Harnessing existing tools like Office macros for nefarious purposes comes with an additional advantage: It can be harder to detect an attack when it comes from a familiar platform. An emailed Word document with macros might not set off the same alarm bells that a strange executable file would. Similarly, PowerShell scripts—which allow IT administrators to make changes to a large number of systems remotely—can be twisted into a destructive force, but aren’t necessarily dangerous on their face.
This resurgence of phishing and social engineering might be a result of improvements in defenses. “It gets harder and harder to fool the computer, but there’s still a good chance of fooling the end user,” said Kevin Haley, the director of Symantec’s Security Response team and a contributor to the report.
As tighter security makes complex exploits harder to come by, hackers may simply be moving on to lower-hanging fruit. Symantec saw a 30 percent drop in the number of web-based attacks in 2016, and the number of zero-day exploits plateaued last year, after a sharp drop the year before. As those fancier attacks get more resource-intensive, sending hundreds of thousands of spam emails remains cheap—and often yields results.
Trends like this one tend to be cyclical, Haley said. As administrators wise up to the email threat and implement tighter security, and people train themselves to stop clicking on fishy links and attachments, simple email-delivered tricks may get less lucrative. “They’re going to keep doing it until it stops working,” Haley said. “And then they’ll move onto something else.”