Different hacker groups claim to have breached servers belonging to ImageShack, Symantec, PayPal and other organizations.
On Sunday, a hacker group called HTP claimed to have compromised Web servers, MySQL databases, routers and management servers used by the ImageShack and yfrog image hosting services.
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"ImageShack has been completely owned, from the ground up," the hackers wrote in a Pastebin post. "We have had root and physical control of every server and router they own. For years."
The post included source code, configuration files, database information, internal network IP (Internet Protocol) assignments and many other details allegedly taken from the hacked ImageShack servers.
ImageShack was targeted in order to test how well the company has strengthened the security of its systems after suffering a security breach in 2009, the hackers said.
ImageShack did not immediately return a request for comment.
In the same post, HTP claims to have hacked servers belonging to Symantec. The leaked data includes information the hackers claim to have copied from a Symantec database, including the names, email addresses and hashed passwords of hundreds of users. Many of the email addresses are on the @symantec.com domain.
"Saved by your WAF [web application firewall]? You wish," the hackers said. "All the other major AV corps are owned too, yours just pissed us off the most. Oh, and if you think we're listing everything here, take the blue pill."
"Symantec is aware of the claims being made online," Katherine James, Symantec's head of enterprise and corporate public relations for EMEA, said Monday via email. "We take each and every claim very seriously and have a process in place for investigating each incident. Our first priority is to make sure that any customer information remains protected. We are investigating these claims and have no further information to provide at this time."
On Sunday, hackers associated with the Anonymous hacktivist collective compromised and defaced various websites including several NBC websites, a Lady Gaga fan site called Gaga Daily and several Australian websites.
On Monday, the group also claimed to have hacked PayPal and published user account information allegedly stolen from the website's database in a document hosted on privatepaste.com. The document has since been removed.
"We're investigating this but to date we have been unable to find any evidence that validates this claim," Anuj Nayar, PayPal's head of public relations, said on Twitter. PayPal did not immediately return a request for comment sent Monday.
The Anonymous hacks were in preparation for or part of the group's scheduled protests on Nov. 5, which is also known as Guy Fawkes Day, primarily in the U.K. One of the group's symbols is the Guy Fawkes mask that appears in the comic book series and movie "V for Vendetta."
Fawkes was a conspirator in a failed plot to blow up the British Parliament in 1605 to kill King James I. He was executed for his role in the conspiracy and ever since it has been tradition to burn effigies of him on Nov. 5.
More attacks are expected from Anonymous members as the day unfolds, as well as a scheduled march during the evening at the Houses of Parliament in London.