A man has been jailed for two years for attacking the websites of Oxford and Cambridge universities and Kent Police.
Lewys Martin, 21, previously of Dover Road, Walmer in Kent, brought down the websites by overwhelming them with requests for information.
Kent Police said he attacked the three websites between 29 January and 2 February last year.
Martin had pleaded guilty to nine offences at a previous hearing at Maidstone Crown Court.
The police website was offline for 1 hour and 17 minutes, Cambridge University's for 1 hour and 20 minutes and Oxford's for 30 minutes at a time.
Police said the universities took the necessary action to prevent the compromise of sensitive information.
Martin admitted five counts of unauthorised acts with intent to impair computer operation, three of unauthorised access with intent to commit other offences and one of unauthorised access to computer material.
"Cyber attacks are a nuisance and cause aggravation as well as costs to countless private and public organisations up and down the country," said Det Con Nicky Holland-Day.
"Most websites have systems in place to prevent them being compromised, and none of those attacked in these instances suffered any more than a temporary disruption."