Websites of political groups fighting anti-gay marriage amendments were hit by a flood of fake traffic Wednesday, in an apparent attempt to muzzle the sites and interfere with a fundraising effort, California's No on Prop 8 group said Thursday.

The Secret Service is now investigating the denial-of-service attack on NOonprop8.com, an attack that began Wednesday afternoon and eventually made the site unreachable that evening, according to spokeswoman Julia Spiess.

No on Prop 8 described the attack as "what appears to be a coordinated attack designed to bring the system down."

Distributed Denial of Service attacks work by sending floods of fake requests to a website in order to prevent legitimate users from getting in. Attackers often use a network of compromised computers — known as a botnet — to send the traffic from multiple locations, which makes filtering more difficult. Motives for such attacks range from revenge to ransom.

As of Thursday morning, the site was back up and running normally after the site's technicians made hardware and software changes, Spiess said.

The attack came right after the group issued a fund raising appeal ahead of the final weekend before Tuesday's vote. The measure seeks to ban same-sex marriages in California, which became legal in June this year after the California Supreme Court struck down the state's laws banning gay marriage, finding them unconstitutional.

The California group says the attack on its site coincided with an attack on Florida's NO on 2 campaign, which opposes a constitutional amendment banning gay marriage.

UPDATE: Geoff Kors, a spokesman for No on Prop 8, declined to speculate on who was behind the attack but had no kind words for the Yes on Prop 8 group.

"I haven't seen the other side condemn the attack, which speaks volumes about the kind of campaign they have run and who they are as people," Kors said.

On Friday, Yes on 8 spokesman Chip White denied any involvement and questioned the report.

"We had nothing to do with it, if in fact there actually was an attack," White said. "There is just so much traffic on the internet that everyone has trouble. As recently as Wednesday morning, our site went down, but we didn't accuse anyone."

Photo: crichton91/Flickr