Schoolchildren must be very wary when using websites such as Wikipedia an official exams watchdog in Britain has warned.
Ofqual (Office of the Qualifications and Examinations Regulator), said Google and Yahoo could be "a good starting point for your research" and pupils should use search engine "advanced options" to maximise results.
It also said students need to be careful when researching pieces of coursework and dissertations, as most do not provide accurate information.
"The on-line encyclopaedia - created using contributions from readers - was not 'authoritative or accurate' and in some cases 'may be completely untrue'," the Telegraph quoted Ofqual as saying.
Children can also be easily tripped up by copying passages from websites containing American phrases and spellings - a clear sign of plagiarism.
The comments were made in a series of documents sent to pupils, parents and teachers warning against cheating at school.
Ofqual also said children could have essays annulled and be banned from examinations for a number of years if caught copying directly from the Internet or fellow pupils.
Teachers were also told to look out for the use of phases and spellings in American English, suggesting pupils had downloaded work from foreign websites.
This includes phrases such as "go get" for "go and get", "have gotten" instead of "have got" and "period" for "full-stop".
Parents are also warned against giving sons and daughters too much help. They should discuss coursework with their children but "not give direct advice on what should or should not be included".
But Ofqual insisted that the guidance should not stop pupils using the Internet.
All passages taken from websites should be referenced, it said, and pupils should rely on authoritative on-line sources such as the Met Office and Hansard when researching work.