Malware Getting Backed Up Along With Data

When malware slips past antivirus, it can get swept up in an enterprise's system backup -- and ultimately reinfect systems when the company restores applications from its contaminated backup.

Oliver Friedrichs, head of Sourcefire's cloud technology group, says this cycle occurs more often than you'd think. Friedrichs recently analyzed data collected from more than 2 million Sourcefire users during a one-month period and found that backup and file restoration applications often inadvertently restore malware.

His findings: During a one-month period, DropBox, a file-sharing and backup cloud-based service, restored 17,705 threats; Maxtor Backup and Restore's MaxSynch, 5,076 threats; 2BrightSparks SynchBack backup software, 165 threats; and FreeFileSync, 104 threats. These were users that had been running traditional AV products.

"We've historically talked about backing up malware as a hypothetical ... we assume it's been happening, but there hasn't been a clear way to see how frequently it's been taking place," Friedrichs says. "This [analysis] is a confirmation and affirmation that it is happening, and we should be concerned about it and aware of backing up malware and then restoring malware."

Friedrichs says this demonstrates how malware is widely bypassing AV and other controls and then getting backed up like any legitimate data or files. Once the backup is "polluted," he says, if they are used to restore a system, they would also be restored onto the system once again.

[Sometimes it's the little things -- a misconfigured network proxy or an unused and forgotten port -- that can make the difference in whether an organization suffers a major hack. See Simple Settings That Could Curtail Some Attacks.]

Is this an AV or a backup problem? Gleb Budman, co-founder and CEO of cloud-based backup service provider Backblaze, says his firm had explored whether it should provide malware scanning as part of its online backup service. But it just didn't make sense for two reasons, he says. "We encrypt all of the files [backed up] so they can't be scanned in our data center," Budman says. "We could scan on your client AV in our backup agent on your system -- we thought about that -- but if a user is already running AV, they would run it, then we would run it, and we'd be using up system resources twice. That seems kind of silly."

Backblaze provides a mirrored backup, continuously backing up data on the fly, he says, so the most recent version, as well as any previous versions, are available for restoration, Budman says. "In our case, the files that we have are files from your computer -- a true traditional online backup concept. We are taking files off, storing them, and giving them back," he says. "With DropBox, they are sharing files between users ... if you want to spread viruses, that would be a vector to spread them."

That's not to say Backblaze couldn't also reinfect a user, Budman says. "We could absolutely back up an infected file," Budman says. "As long as they don't open it, they won't be infected because it's just the file. ... If they run AV and realize they were infected and clean that document, they can upload a clean version and replace it on our [backup] system."

Backblaze, whose customers range from small to midsize businesses to consumers, lets users even roll back to an earlier time and restore a file to just before it got infected, for example, Budman says.

"It's possible to get an infection from a backup, but it's also avoidable," he says. "Online backup of data -- if you're doing it continuously -- is probably the safest way to do it" because it takes a snapshot of the data and doesn't include the system files and registry, for example.

The underlying problem of reinfection via backup restoration is AV missing so much malware, with AV efficacy rates less than 50 percent, Friedrichs says. "This situation is becoming increasingly common -- and it's incredibly risky for enterprises whose users are asked to do backups and then reconnect to the network. Some have talked about this happening anecdotally over the years, but until now it was hard to quantify where and when this happens," he wrote in a blog post recently.

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