Not-for-profit organisation Get Safe Online has offered security tips on how to protect yourself on the internet.
More than half the people in London have been targeted by criminals online and the average cost of a successful attack is £274 a time.
The figures, which are the highest in the country, were revealed by Get Safe Online.
The organisation surveyed 2,000 consumers in the capital and found that 57% of Londoners had been targeted by online criminals.
Eighteen per cent of those questioned admitted they were too embarrassed to tell anyone or share their experience with others.
This may explain why a third of us (33%) claim to having no idea whether we are putting ourselves at risk, a further 39% of us admit we really needed to know more about being safe online and 29% don't know if they are being safe online.
Here are some online safety tips offered by Get Safe Online:
Divide security and protect both your hardware, such as PCs or mobile devices as well as protecting yourselves as individuals.
Stay safe on your PC or mobile, that means making sure your antivirus software is updated with the latest version, so that your operating systems are up to date and that you have a firewall as well.
It is about being aware of the scams that are out there. Ranging from being able to spot a phishing email, to avoiding cold call telephone sales from people pretending to be security vendors.
The increase in social media is a big area too. We need to be vigilant about who we share our details with online.
People often forget to be secure on smartphones as security here is even more critical here especially now people access bank details from their phones regularly.
For more information visit Get Safe Online.
The top five most common consequences of an online attack:
Having to change all of your online passwords (40%)
Wasting valuable time trying to fix the problem (37%)
Left feeling red faced (18%)
Replacing bank or credit cards (16%)
Losing money (8%)
In spite of the number of attacks in London, the survey uncovered that it has not changed people's behaviour. Of those who experienced an attack, the majority continued to use their laptops, tablets, and smartphones in the same way.
Despite more than one in 10 Londoners having their social media accounts hacked, only half of respondents (51%) use the highest levels of security on the social networking site Facebook and one in 10 (10%) are not even aware that you can change your security settings.