The most harmful websites on the Internet, as far as risk of malware infection goes, are religious in nature, according to Symantec"s annual Internet Security Threat Report. Sorry, porn sites.
The malware content is (usually) not intentional on the website owner"s behalf, but is instead hosted on sites that have been compromised and infected.
Symantec"s report, now in its 17th volume, says that religious websites have 115 threats on average, mostly in the vein of fake antivirus software. Pornographic websites, in comparison, have less than a quarter of that number, averaging about 25 threats per website. However, there are obviously many more pornographic websites on the Internet than there are religious websites.
Pornographic websites ranked 10th overall for percentage of infected websites, after other categories of sites like shopping, education/reference, technology, entertainment and more. The number one most frequently exploited category of websites is blogs and web communications sites.
The report hypothesizes that the reason for this disparity in threats per infected site is that because porn website owners are already making money from the Internet, they have a vested interest in keeping their source of income free from malware. A bad user experience is not good for repeat business, naturally.
The full report can be viewed in PDF format (5.60 MB).