Meanwhile, protesters suspect they might be infiltrated themselves. The Patriot Act, passed in reaction to the Sept. 11, 2001, terror attacks, broadened the government's domestic spying powers and some protest organizations believe they are routinely infiltrated.
"Infiltration was understood once we applied for a permit," said Louie Jones, an organizer for Still We Rise Coalition, a group of 35 local community organizations holding a march on the first day of the GOP convention. Jones said he believed infiltrators were mainly there to collect intelligence, and said his organization had nothing to hide.
However, other protesters fear that certain infiltrators might do more than just keep watch. Some may be agents provocateurs — double agents that will incite violence and ruin the prostesters' public image.
Protesters say the spectacle of riots during the 1968 Democratic National Convention in Chicago, and later, during the World Trade Organization talks in Seattle in 1999, distracted the public from any calls for change.
"Since Seattle, every protest in the U.S. has been marred by this image of broken Starbucks windows," said Angela Coppola of No RNC Clearinghouse, a protest organization.
After Hajicek posted his warning on DailyKos.com, one respondent said, "This sort of sabotage isn't new." The respondent recounted signing up for a locally-organized screening of the anti-Fox News film Outfoxed in Washington, D.C. "When I arrived, there was a crowd of people on the sidewalk and the address didn't exist."
Some discussion members expressed fears that a coordinated effort was under way to disrupt the protesters.
Mark Libkuman, a developer at CounterConvention.org, says the site's organizers have removed 30 to 40 listings they suspected were fake offers for accommodation in New York. "Some were very witty," he said, "but they didn't do much for the usefulness of our site."
The site has since instituted a registration process that deters would-be pranksters, and Libkuman and his colleagues screen the listings and spot most of the fake ones right away, he said. He said the listing that snared Hajicek was the only one he is aware of that stayed on the site and caused disruption.
On the other hand, members of the FreeRepublic.com discussion board discovered Hajicek's frustrated trip to New York and were buoyed by the account. One applauded the hoaxer: "If you did this on purpose, this is truly 'Hall of Fame' material. Beautiful!"
A Poorly Conceived Prank
For Hajicek though, taking an early bullet in this secret war hasn't turned out so badly.
After ABCNEWS.com sent an e-mail to Hajicek's purported host asking to speak to him, Hajicek's purported host sent a contrite e-mail to Hajicek to "profusely apologize for any inconvenience."
"It was a poorly conceived bad prank gone way too far," the hoaxer wrote in the e-mail, which Hajicek provided to ABCNEWS.com. The hoaxer did not respond directly to ABCNEWS.com's e-mails. A woman who answered the phone at the number he provided to Hajicek denied any knowledge of the prank.
As a result of his warning, Hajicek says he received dozens of offers of places to stay, and is planning to go to New York after all. He even received some money as a measure of sympathy. He now has a reservation at a hotel off Times Square, just blocks from the Republican Convention.