The head of internet security at the Cabinet Office has told people to use fake names online – leading to claims that his advice would help encourage crime.

Andy Smith told a conference in Whitehall that using pseudonyms for social networking was "a very sensible thing to do" as real identity details could be used against internet users. "When you put information on the internet do not use your real name, your real date of birth," Mr Smith told the Parliament and the Internet Conference in Portcullis House. "When you are putting information on social networking sites don't put real combinations of information, because it can be used against you."

Despite several past examples of government agencies losing personal data on laptops and memory sticks, however, he added: "When you are interacting with government, or professional organisations – people who you know are going to protect your information – then obviously you are going to use the right stuff."

Mr Smith's comments were supported by Lord Erroll, chairman of the Digital Policy Alliance. But Labour MP Helen Goodman told the BBC that his words were "totally outrageous", saying she had been contacted by victims of internet trolls using false names.