The number of registrations for websites with a .org domain name rose by more than a quarter in the first six months of 2009, according to web hosting firm Fasthosts.
The firm said it registered 27 per cent more new sites with the .org suffix between January and June than during the same period last year.
It said there was higher demand for the .org domain than for any other non-business domain, such as .net or .info.
A spokesman for the organisation told Third Sector the increase was caused by a growing number of small, local charities and social activism groups creating websites to increase awareness of their causes.
He said it was also due to an increase in the number of microsites, specialised websites that run alongside charities' main websites to raise awareness of a specific area of their work.
Fasthosts declined to reveal precise figures on the scale of the increase, but said the figure represented "thousands more" new registrations for .org websites in the first half of 2009 compared with the same period in 2008.
The firm's spokesman said there was no guarantee that all of the .org sites were for legitimate not-for-profit groups because there were no regulations governing who could be awarded a .org address.
Fasthosts' in-house fraud department had not noticed an increase in reported cases of fraudulent charity sites over the past year, he added.