Can a hacker use a brute-force attack to steal an online password?

Given enough time and computing power, a brute force attack can theoretically crack any password.

Harish Kumar asked if a brute force attack--which tries random text strings until one turns out to be your password--would work on major websites. "Will Facebook allow millions of failed attempts?"

We all know that cybercriminals successfully hack Facebook, Twitter, Google, and Microsoft accounts. In one recent three-day period, two readers emailed me for advice on recovering their hacked Twitter accounts. (I point them to Your Twitter account has been hacked! Here's what to do about it.)

[Email your tech questions to]

Most successful attacks come not from brute force but from social engineering--tricking you into giving away your password. It doesn't work with everybody, but it works with the gullible. For more on this, see Christopher Null's The moral of the Twitter-GoDaddy breach: People are the easiest thing to hack.

As a rule, websites don't lend themselves to brute-force attacks. Each guess at a password will take several seconds to come up true or false. At that rate, even hacking a four-digit number could take 15 to 20 hours. And long before that, any decently-designed site will recognize what's going on and shut down the account.

Yet people claim to have successfully done it, finding ways to bypass all of the safeguards. See How to Brute Force hacking Facebook in Kali Linux for one such claim.

And no, I didn't try it. I suspect that if this technique ever worked, it doesn't anymore. Facebook would immediately plug whatever vulnerability made it possible. Of course, that's no guarantee that other flaws won't be discovered in the future.

Keep in mind that if you turn on Facebook's Login Approvals (which you'll find on the Security Settings page), someone who steals your password still won't have access to your account. With this two-step verification, accessing your account requires not only your password but also your cellphone (not the number, but the actual phone).

But if brute force isn't practical, why bother with strong passwords? The whole point of creating a very long and difficult password is to make a brute force attack impractical. (See Learn to use strong passwords for more on this.)

I put that question to security expert Bruce Schneier. He told me that "Regardless of what else is going on, I would choose a long and difficult password for anything important."

I agree. On one level, it's simply a good habit. And besides, it's one more layer of protection in a world where we never know when another layer will be peeled away.

Join the CSO newsletter!

Error: Please check your email address.

Tags securitypasswords

More about FacebookGoogleLinuxMicrosoft

Show Comments

Featured Whitepapers

Editor's Recommendations

Solution Centres

Stories by Lincoln Spector

Latest Videos

  • 150x50

    CSO Webinar: The Human Factor - Your people are your biggest security weakness

    ​Speakers: David Lacey, Researcher and former CISO Royal Mail David Turner - Global Risk Management Expert Mark Guntrip - Group Manager, Email Protection, Proofpoint

    Play Video

  • 150x50

    CSO Webinar: Current ransomware defences are failing – but machine learning can drive a more proactive solution

    Speakers • Ty Miller, Director, Threat Intelligence • Mark Gregory, Leader, Network Engineering Research Group, RMIT • Jeff Lanza, Retired FBI Agent (USA) • Andy Solterbeck, VP Asia Pacific, Cylance • David Braue, CSO MC/Moderator What to expect: ​Hear from industry experts on the local and global ransomware threat landscape. Explore a new approach to dealing with ransomware using machine-learning techniques and by thinking about the problem in a fundamentally different way. Apply techniques for gathering insight into ransomware behaviour and find out what elements must go into a truly effective ransomware defence. Get a first-hand look at how ransomware actually works in practice, and how machine-learning techniques can pick up on its activities long before your employees do.

    Play Video

  • 150x50

    CSO Webinar: Get real about metadata to avoid a false sense of security

    Speakers: • Anthony Caruana – CSO MC and moderator • Ian Farquhar, Worldwide Virtual Security Team Lead, Gigamon • John Lindsay, Former CTO, iiNet • Skeeve Stevens, Futurist, Future Sumo • David Vaile - Vice chair of APF, Co-Convenor of the Cyberspace Law And Policy Community, UNSW Law Faculty This webinar covers: - A 101 on metadata - what it is and how to use it - Insight into a typical attack, what happens and what we would find when looking into the metadata - How to collect metadata, use this to detect attacks and get greater insight into how you can use this to protect your organisation - Learn how much raw data and metadata to retain and how long for - Get a reality check on how you're using your metadata and if this is enough to secure your organisation

    Play Video

  • 150x50

    CSO Webinar: How banking trojans work and how you can stop them

    CSO Webinar: How banking trojans work and how you can stop them Featuring: • John Baird, Director of Global Technology Production, Deutsche Bank • Samantha Macleod, GM Cyber Security, ME Bank • Sherrod DeGrippo, Director of Emerging Threats, Proofpoint (USA)

    Play Video

  • 150x50

    IDG Live Webinar:The right collaboration strategy will help your business take flight

    Speakers - Mike Harris, Engineering Services Manager, Jetstar - Christopher Johnson, IT Director APAC, 20th Century Fox - Brent Maxwell, Director of Information Systems, THE ICONIC - IDG MC/Moderator Anthony Caruana

    Play Video

More videos

Blog Posts