If your computer’s been hacked, Dale Drew might know something about that.

Drew is chief security officer at Level 3 Communications, a major internet backbone provider that’s routinely on the lookout for cyber attacks on the network level. The company has linked more than 150 million IP addresses to malicious activity worldwide.

That means all of those IP addresses have computers behind them that are probably involved in distributed denial-of-service attacks, email spam, or breaches of company servers, Drew said.

Hackers have managed to hijack those computers to “cause harm to the internet,” but the owners don’t always know that, Drew said.

The tracking capabilities of Level 3 highlight how ISP s can spot malicious patterns of activity over the internet, and even pinpoint the IP addresses that are being used for cyber crime.

In more extreme cases, Level 3 can essentially block bad traffic from harassing victims, and effectively shut down or disrupt the hackers’ attacks.

So why aren’t ISP s doing more to crack down on cyber crime? The issue is that an ISP ‘s ability to differentiate between normal and malicious internet traffic has limits and finding ways to properly respond can open a whole can of worms.

Malicious patterns

Level 3 has built up a database of 178 million IP addresses — most of them static IP addresses — that it has connected to suspected malicious activity. It’s done so by pinpointing patterns that deviate from “known good” internet traffic, Drew said. He compared it to running a post office. Although Level 3 isn’t examining the content of the internet traffic or the “envelopes” passing through, it does know who’s sending what and to whom.

For example, “every time this user gets a red envelope from person X, they complain its spam,” Drew said. “So I can start to build a heuristic off that behavior.”

Bad-behavior patterns have helped Level 3 build algorithms to identity suspicious traffic. Of the millions of IP addresses it’s been tracking, 60 percent are likely associated with botnets, or armies of infected computers that can be used for DDOS attacks.

Level 3 has associated another 22 percent with email phishing campaigns.

One might wonder why Level 3 doesn’t just block these IP addresses from the internet. But that can be problematic. Often, users of hacked computers are unaware their machines have been compromised, and it may be unclear whether some of those machines are also being used for important purposes, such as legitimate financial transactions.

Blocking those machines could potentially mean stopping millions of dollars in transactions, Drew said.

Instead, the company tries to notify the users of those IP addresses. In many cases, they are businesses, which can be quick to respond, Drew said. However, when it comes to consumers, there’s no phone book linking one person to an IP address. So Level 3 has to work with the hosting provider in order to reach the user.

Confronting the limits

Overall, it can be an uphill battle. “For every IP address we repair, more IP addresses are being compromised,” Drew said.

Other ISP s, including some in Europe, have also been notifying customers when their machines might be infected. It’s become a years-old, growing practice, but getting users to fix their infected computers isn’t always straightforward, said Richard Clayton, a security researcher at the University of Cambridge and director of its cloud cyber crime center.

Even when ISP s send warning messages to users, what then? Not every PC user knows how to resolve a malware infection, Clayton said. For ISP s, it can also be a matter of cost.

“Of course we want to see ISP s helping, but they are in a competitive market,” he said. “They are trying to cut their costs wherever they can, and talking to customers and passing on a message is not a cheap thing to do.”

In addition, ISP s can’t identify every malicious cyber attack. Most hacking attacks masquerade as normal traffic and even ISP detection methods can occasionally generate errors, Clayton said.

“If you have a 99 percent detection rate, in an academic paper, that sounds fantastic,” he said. “But that basically means one out of 100 times, you’ll be plain wrong.”

No magic bullet

That’s why taking down suspected hackers usually requires collective action from law enforcement and security researchers who have thoroughly investigated a threat and confirmed that it is real. Governments and ISP s have also become involved in creating websites and services telling users how to effectively clean up their PCs.

It’s a difficult balancing act for ISPs, said Ed Cabrera, the chief cyber security officer at antivirus vendor Trend Micro. “They can do a lot of detection quite easily,” he said. “But the blocking piece is not something that they want to take responsibility for.”

Cyber criminals are also continually elevating their game, making them harder to detect. “The problem is nowhere near black and white,” Cabrera said. “We’re quick to say ISPs aren’t doing enough, but I think often times that’s unfair.”

Level 3’s Drew said it’s tempting to think that the world’s cyber security problems can be solved with a magic bullet. But for now, it will take a collective effort — of ISP s, governments, businesses and consumers — to clean up the internet and secure today’s devices.

“Even if we were able to deploy exhaustive technology to analyze the bad, ugly traffic, it still doesn’t fix the infected devices,” Drew said. “The end user still has a role to properly patch that device.”

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