Facebook on Monday began warning users if they are about to visit a malicious URL. As part of a partnership with security firm Websense, each time a user clicks on a link within Facebook, the address will be checked against a database of known malicious sites. If the link matches a known bad site, users will be presented with a page that offers the choice of continuing on, returning to the previous screen or learning why the link was classified as suspicious. Cybercriminals have flocked to sites like Facebook in recent years. A new Ponemon Institute survey of more than 4,000 IT and IT security professionals found that 52 percent have faced an increase in malware as a result of social media.