Three-quarters of all Web sites that try to foist malicious software on visitors are legitimate sites that have been hacked, a report released today found. Even worse, most of these compromised sites are social networking communities and some of the Internet’s most popular destinations. Those numbers come from stats (PDF) collected in the first six months of this year by Websense, an online security company that scans more than 40 million Web sites hourly for signs that they may have been compromised by hackers. Websense found that 60 percent of the Top 100 most popular sites this year have either hosted malware or forwarded visitors to malicious sites. The company also says that nine out of 10 of those compromised sites were social networking or Web search sites. “The majority of these attacks are using Web properties as repositories for malware, mainly because they let users upload content,” said Dan