MANILA, Philippines -- Blogs are the riskiest websites to visit because these are the biggest sources of viruses on the Internet, according to antivirus firm Sophos.

As end-users become more aware about viruses via email, hackers are instead embedding viruses into websites that threaten unsuspecting visitors.

On average, Sophos detected more than 16, 000 malicious web pages every day -- or one every five seconds -- during the first six months of 2008. This is three times faster than last year’s figures.

In its report, Sophos noted that the number one host for malware on the Web is Blogger, which allows users to create blogs for free (with URLs that end in "blogspot.com").

Sophos estimates that blogs created on Blogger account for two percent of infected webpages.

According to Sophos, hackers either set up malicious blogs using Blogger, or place comments into unsuspecting blogs that contain links to websites that contain viruses.

Aside from blogs, Sophos noted that more than 90 percent of webpages that are spreading Trojan horses and spyware are legitimate websites, some even belonging to Fortune 500 companies that had been hacked using a method called SQL injection.

SQL injection exploits security vulnerabilities and inserts malicious code into the database running a website. Users who then visit these affected websites risk having their computer taken over by hackers and have personal data stolen.

Companies whose websites have been struck by such an attack often clean up their database, only to be infected again a few hours later, Sophos reported.