Don't reuse your PIN codes, security expert warns. Hackers want your passwords, and they will use any method to get them. From sophisticated Gmail attacks that appear to come from Google itself, the use of infostealer malware, and even deploying automatic password hacking machines. The last thing you want to do, therefore, is make their task any easier. Yet, sadly, that’s exactly what millions of smartphone users, both Android and iPhone, are doing. Here’s why one is the magic number when it comes to your PIN, and ignoring this simple advice could leave your phone and your accounts open to hacking threats. ForbesSamsung Galaxy Password Warning For Millions — Act Now, What To DoBy Davey Winder The Smartphone PIN Problem Keeping your iPhone or Android device secure is a no-brainer. We all know that it is the key that opens a treasure trove of valuable data for hackers, scammers, and criminals of all types. It’s madness, then, that just four numbers sit at the forefront of smartphone defense for millions and potentially billions of users. Yes, I’m talking about your lock screen PIN. OK, biometrics, be that by way of fingerprint or facial recognition, add a layer of much more secure protection over this, but underneath, there’s your PIN. And for most people, that means four numbers. My PIN, by the way, is 10 digits long because you don’t have to stick to the four-digit format, and the longer the number, the more secure the defense. Unless, that is, you make one cardinal mistake. “I’d never use the same PIN or password twice,” Chiara Cavaglieri, a senior researcher at Which?, warned. “If an attacker has got hold of your login details for one online account,” Cavaglieri explained, “perhaps following a data breach, or stolen through a phishing message, they will use automated software to test these login details across other accounts.” And that includes your PIN, used not only to secure your smartphone but your bank cards at an ATM and often, still, other accounts. One is, quite literally, the magic number when it comes to PIN codes — use them once and never repeat across accounts, cards and devices. And this is where it gets really sticky for smartphone users who don’t follow this sage advice. Shoulder-surfing thieves will take the opportunity to observe you entering a PIN number into your device when the occasion presents itself. We all know that biometric unlocking doesn’t work every time, so they can then grab your Android or iPhone and use this to unlock it and change security protections where possible. The threat goes beyond the hardware theft; if you have reused that PIN, it opens up the door to further attacks. If you keep your bank card and your phone in the same wallet case, you really could be in for an expensive day. MORE FOR YOU WWE WrestleMania 41 Results, Winners And Grades On Night 2 NYT Mini Crossword Hints, Clues And Answers For Monday, April 21 Pope Francis Has Died At 88, The Vatican Says The simple security advice is usually the best. So, change your PIN codes now to ensure they are all unique and, if you want to be extra secure, try using a longer PIN code to protect your smartphone, or even a simple password to confuse thieves even more. ForbesNew Gmail And Microsoft 2FA Security WarningBy Davey Winder Follow me on Twitter or LinkedIn. Check out my website or some of my other work. Editorial StandardsForbes Accolades