The hacktivist group Anonymous made good on its promise of digital retaliation against a Californian Police Department for the force it used against protesters this week.

A distributed denial-of-service attack against the Oakland Police Department's website took the site down for several hours.

In addition, members of the collective have began releasing information about Oakland police officers.

"The time has come to retaliate against Oakland police via all non-violent means, beginning with 'doxing' of individual officers and particularly higher-ups involved in the department's conduct of late," read an Anonymousstatement, posted to Pastebin. Doxing refers to the public release of information about individuals.

Anonymous' operation, dubbed "OpUprise," came in response to the actions of Oakland police on Tuesday trying to squash a largely peaceful demonstration organised to protest at the clearing of an "Occupy Oakland" encampment.

Police used tear gas, rubber bullets and flash grenades against the demonstrators, according to reports and video posted on YouTube. Authorities have said the response was warranted because some of the rally participants were throwing objects at them.

The most seriously injured victim was Scott Olsen, an Iraq War veteran, who suffered a fractured skull after being struck by a police projectile.

According to the Pastebin document, Anonymous is offering a "no questions asked" $1,000 reward for information about the officer who threw the projectile at Olsen.