"Many malicious URLs are now invisible to URL filters and antivirus software alike, a web security company has found after conducting its own tests.
Web security company M86 Security pitted three leading but unnamed antivirus products against 15,000 malicious URLs and found that only 39 percent were successfully blocked. When they ran a second set of malicious URLs against a leading URL list the news was even worse. Only 444, or around 3 percent, were correctly identified." – Content courtesy of Antivirus software often foxed by malicious URLs – Techworld.com