Virus authors have tapped into excitement over the latest Harry Potter film to spread an old worm.

Netsky.P was the second most common virus in May, according to figures from anti-virus companies. Now the worm seems to have found new life by enticing young computer users with promises of material relating to the Hogwarts hero.

While there is nothing sophisiticated about the worm's technique, innocent youngsters have been opening the attached file and letting Netsky.P wriggle on to the family hard disk.

The email arrives with an attachment that has the words 'Harry Potter' in the file name. Parents have been warned that the virus is also appearing on file-sharing sites.

Ensure your anti-virus software is up to date and make sure any children using your computer are aware of the problem.