Mobile broadband users are unaware of their download limits, leaving them open to hefty charges from their mobile networks.
Price comparison site moneysupermarket.com conducted a survey, which showed that 54 per cent of users didn't know what their download limit was and almost a quarter didn't even know they had one.
James Parker, manager of mobiles and broadband at the website, said: "Dongle users are most at risk of incurring charges from exceeding download allowances as limits on dongles tend to be much lower than fixed line packages."
According to Parker, a user with a 3GB limit on an O2 dongle could end up paying 200 for every extra GB they download and a 3 user would incur a 100 charge per GB.
Both firms do text the user once they have reached their limit.
Other companies, like Vodafone, Orange and Virgin, charge closer to 15 with T-Mobile the only one that does not charge at all.
Parker concluded: "Whilst the portability is great, users need to be aware that dongles are most suitable for light users, fixed line is a better value option for heavy users."
