GOOGLE has warned users that billions of passwords – and hundreds of thousands of username and password combinations – have been hacked.

Cyber-experts are now urging users to make sure they're using tough passwords that haven't already been stolen.

5 Google released this handy "how to" to help you get started Credit: Google

Earlier this year, Google launched a Password Checkup add-on for the Google Chrome web browser.

It displays a warning whenever you sign in to a website using "one of over 4billion usernames and passwords" that have been hacked.

Google does this by cross-referencing your log-in details for different sites with a huge list of hacked log-ins.

"Since our launch, over 650,000 people have participated in our early experiment," Google's Jennifer Pullman explained.

5 These are the WORST passwords of 2018 – so don't ever use them

"In the first month alone, we scanned 21million usernames and passwords and flagged over 316,000 as unsafe – 1.5% of sign-ins scanned by the extension."

There's obviously a huge risk for anyone whose username and passwords from different sites have been hacked.

It's important to immediately change your log-in details to stay safe.

But even passwords uploaded online without associated usernames can put you at risk.

If you use a very simple password, it's likely someone else does too – and they may have been hacked themselves.

Hackers buy huge lists of these compromised passwords from lots of different sites because people often re-use them.

So hackers are much more likely to gain access to an account by forcing a long list of "known" hacked passwords than trying random letters or numbers.

"Hijackers routinely attempt to sign in to sites across the web with every credential exposed by a third-party breach," said Pullman.

"If you use strong, unique passwords for all your accounts, this risk disappears."

5 Google's Chrome extension will show this warning if you're using a breached password Credit: Google

5 Google data shows that users most often re-use vulnerable passwords on shopping, news and entertainment sites Credit: Google

Password safety – the expert advice Here's what Javvad Malik, cyber expert at KnowBe4, told The Sun... "Despite all their weaknesses, it looks as if passwords will stay for the foreseeable future.

"But there are some steps people can take to strengthen their passwords so that it is less likely hackers can break into their accounts.

"Perhaps the most important step is to not re-use the same password across different websites.

"It is convenient only having one password, but this means that if someone guesses, or steals one of your passwords, they can then use that to gain access to any of your other accounts.

"Using a password manager can help create and remember all the different passwords.

"Failing that, even writing passwords down can be good in some cases (just don't leave your notebook lying around).

"The second step is to take advantage of two factor authentication (2FA) wherever it is available.

"For many sites that offer this service, in addition to entering username and password, it will send a code via text message to your phone which will need to be entered.

"Third, and finally, people should be wary of the scams which try to steal their passwords.

"For example, receiving an email with a link from a large provider such as Microsoft, Amazon, or Apple, and asking people to re-enter their username and password or risk having their account frozen.

"People should never click on such links in emails, and only navigate manually to any sites they wish to visit if they need to log onto their accounts."

How to check your password

The free Password Checkup software can be loaded onto Google Chrome and lets you know if your account details have been compromised in a cyber attack or data breach.

Once installed, the Chrome extension runs in the background of your browser and checks any login details you used.

If your password or username matches a Google database of more than 4billion compromised credentials, the software will flag them.

An alert that pops up on your screen reads: "Password Checkup detected that your password for [website] is no longer safe due to a data breach. You should change your password now."

If a new data breach occurs, the tool will let you if any of your passwords were compromised the next time you login to Chrome.

It gives you any exposed accounts in a small list that you can click through to change your passwords.

All information is encrypted, and Google says it has no way of seeing your data.

"We built Password Checkup so that no one, including Google, can learn your account details," Google said.

"Password Checkup was built with privacy in mind. It never reports any identifying information about your accounts, passwords or device."

You can download Password Checkup from the Chrome webstore by clicking here.

Alternatively, popular web-tool Have I Been Pwned also lets you check if you've ever been hacked.

5 This chart reveals the percentage of safe or unsafe passwords – and reveal how much safer "new" passwords are against guessing attacks Credit: Google

Largest breaches – hacked passwords uploaded online Here's Have I Been Pwned's list of largest online breaches... Collection 1 accounts – 772,904,991 breached accounts leaked

Verifications.io accounts – 763,117,241 breached accounts leaked

Onliner Spambot accounts – 711,477,622 breached accounts leaked

Exploit.In accounts – 593,427,119 breached accounts leaked

Anti Public Combo List accounts – 457,962,538 breached accounts leaked

River City Media Spam List accounts – 393,430,309 breached accounts leaked

MySpace accounts – 359,420,698 breached accounts leaked

NetEase accounts – 234,842,089 breached accounts leaked

LinkedIn accounts – 164,611,595 breached accounts leaked

Dubsmash accounts – 161,749,950 breached accounts leaked

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In related news, cyber-experts recently warned that hackers could hijack your phone to inflict tinnitus, and even melt your gadgets using "sonic warfare".

New hacked iPhone cables let crooks completely hijack your gadgets.

And a shock Instagram blunder let strangers secretly download your photos, videos and location – with "millions of users" affected.

Do you think your passwords are tough enough? Let us know in the comments!

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