Thousands of National Lottery accounts have been put at risk of being 'hacked', operator Camelot said.
Here is how you can keep your details safe online.
- Keep your details secure
Never share login details for your banking or other secure sites with anyone else, whether in person, on the telephone or online.
Watch out for phishing emails that include links to fake login pages that will steal your details and for phone scams by fraudsters posing as bank workers.
Be aware that no reputable organisation should ever ask you to reveal your full password.
- Create strong passwords
It's an obvious tip - but one that many ignore.
Strong passwords should contain a mixture of letters, numbers and special characters such as punctuation marks.
Avoid using obvious or guessable information such as family names, former pets or dates of birth - many of which you may have already shared on social media.
It's also strongly recommended that you use a different password for every website and update passwords regularly.
- Ensure all your networked devices are protected
The average household has a steadily growing number of networked devices, ranging from baby monitors to smart appliances and networks allowing users to control utilities such as lighting or heating via mobile phones.
It's vital that all of these are password protected, otherwise they can be hacked and taken over.
The consequences of failing to secure all your networks could range from appliances being hijacked to stage hack attacks to strangers being able to watch children via baby monitors.
- Use antivirus software and firewalls
Another basic but key tip - ensure that you have antivirus and anti-spyware security in place and up to date at all times.
Choose a reputable programme to scan emails, monitor files, scan your computer and protect you from dangerous downloads.
- Beware of public wifi
Hackers can use unsecured public wifi zones to target other users on the network and they can also set up fake hotspots to harvest information.
When out in public, avoid using public zones set up by unknown users and which don't require a password to login.
Ensure that you log off when you have finished browsing - and it's best practice not to send personal information via a public network.
- Stay aware
Finally, be aware that if something looks or sounds suspicious then it may well be.
Hackers and phishers are producing increasingly sophisticated attacks, but if you get a strange bill or an unusual demand for personal information out of the blue, then be prepared to hold back information and ask questions.
If in doubt it's always better to refuse to hand over data or make payments until you have contacted the organisation purporting to be making contact and checked that it is legitimate.