Food and drink companies that target children through advertising on the internet have been warned that they must self-regulate their marketing practices, or risk having regulation imposed on them. Since Ofcom's restrictions on advertising foods that are high in fat, sugar and salt to children on television came into force on 1 July, many leading manufacturers have targeted young people through social networking sites and company web pages, according to the Chartered Institute of Marketing (CIM). But the shift could simply lead to a similar clampdown on online advertising, said David Thorp, director of research and information at CIM. "Marketing is a powerful tool for changing attitudes but UK companies need to make sure it is a positive force for change, by encouraging children to eat more healthily," said Thorp. "It is much better that we take the lead on this issue as it gives marketers the opportunity to set perimeters. If we don't, we face these being set for us." He added: "It also shows we are serious about the issue. Responsibility no longer ends at the retailer's shelf and those who market to children must look for ways of promoting a more healthy diet and lifestyle." The Department of Health confirmed it had spoken to many food and drink advertisers to express its concerns about HFSS food advertising on the internet. It is now closely monitoring online activities to help it decide whether legislation was necessary, said a spokeswoman. Food and drink companies using the internet, including social networking sites, have come under parrticular fire from campaigners this week. "I don't think it is a legitimate tactic to shift their advertising in this way," said head of the Sustain campaign Richard Watts. "If Ofcom thinks under 16-year-olds should be protected, that is a principle which should be carried through to other media." A spokeswoman at the Consumer Assocation said food companies were focusing their efforts to entice children on areas that were not covered by the rules. Mars has been singled out for criticism because it placed a profile for its Skittles brand on the Bebo website.