Internet users have been hit by a widespread web attack that has compromised thousands of sites, including pages belonging to the Wall Street Journal and the Jerusalem Post.
Estimates of the total number of compromised websites vary between 7,000 and 114,000, according to security experts. Other compromised sites include Servicewomen.org and Intljobs.org.
Cisco Systems' web-tracking subsidiary, ScanSafe, started following the incident two days ago, said Mary Landesman, a senior security researcher with Cisco.
Somehow, the hackers have posted malicious HTML code on the affected Web sites that redirects victims to a malicious Web server. This server tries to install software on Web visitors' computers. If it's successful, the software gives the criminals a way to remotely control their victims' PCs.
Security researchers are still gathering data on the attacks, but they suspect that hackers used what's known as an SQL injection attack to trick the Web sites into running database commands, which ultimately gave the hackers a way of installing their malicious HTML.
All of the infected sites appear to be using the Microsoft Internet Information Services Web-server software running with Active Server Pages, according to researchers at Sucuri Security.
Although these mass Web attacks have become relatively common in the past three years, this incident appears to be the worst since a large number of Wordpress-based sites were hacked in April, said Andre DeMino, a co-founder of the Shadowserver malware-tracking group.
Many of the hacked sites have been compromised before, Landesman said. She believes that just 7,000 sites have been hit. Sucuri put the number at 114,000.
Not all affected sites are thoroughly compromised, Landesman added. On some very large websites, attackers were able to install their code only on certain pages, rather than the entire site. Often, hackers get limited access because they break into a partner site - an ad company, for example - that is allowed to post on certain parts of the larger company's website.
On the Wall Street Journal, for example, only a small number of pages that displayed real estate ads were hit. The Wall Street Journal had no immediate comment on the incident, but a spokeswoman said she was looking into the matter.
Antivirus vendor Sophos said it had spotted the attack on the Jerusalem Post's Web site.
HP and Microsoft have released a free tool called Scrawlr that helps users check their Web sites for SQL injection vulnerabilities.
"The SQL injection attacks that allow the systems to be compromised are occurring due to vulnerabilities in third-party web applications and do not demonstrate vulnerabilities in Microsoft software," said Microsoft spokesman Jerry Bryant.
"We do offer guidance for developers on how to code applications so they are protected against SQL injection," he added.