The majority of the web’s most visited sites pose security threats, according to research by security vendor Websense.

The research found that during the last year, 61 of the Internet’s top 100 sites were either hosting malicious content or containing a masked redirect to a malicious website.

The number of malicious websites on the Internet has grown almost 700% on the same time last year, and 77% of these are legitimate sites that have been compromised by malicious code. The study found that many of these breaches were the result of three large-scale SQL injection campaigns, named Gumblar, Beladen and Nine Ball, which utilised ‘drive-by’ exploits to install Trojan downloaders on more than 40,000 legitimate websites.

Websense also reported that the total volume of email containing viruses increased 600% in the month of June. In addition, the automated submission of blog and forum comments containing links to malicious web pages increased; the security firm estimated that 95% of all user-generated comments are spam or malicious.