Sponsorship deals and ticketing are said to be under threat
International criminal networks are already preparing to target the 2012 London Olympics, a senior Metropolitan Police officer has warned.
Deputy Assistant Commissioner Janet Williams said several "front companies" were under investigation by police.
She told an Association of Chief Police Officers conference that criminals may also be preparing electronic attacks on sponsorship deals and ticketing.
She said the force would need more Home Office money to deal with "e-crime".
"We are starting to see some precursor activity, we are starting to see companies being set up in what we believe are false names in anticipation of fraud and other types of criminal activity during the run-up to the Olympics," she told the Acpo annual conference.
Ms Williams said cyber criminals were determined, sophisticated and flourishing.
The Metropolitan Police has established a specialist team to examine the threat of electronic and internet attacks on the 2012 Games.
She said networks have in recent months targeted London hospitals, police forces and major private companies, including well-known online shops.
Ms Williams said: "Very recently we have had three London hospitals badly affected, that was identified as computer viruses overloading the systems."
The conference meeting heard that three million online crimes take place in Britain every year, about one every 10 seconds.