Websense security researchers uncovered an unusual extortion plot when a corporate customer fell victim to a virus that encrypted documents, photographs and spreadsheets, leaving behind a ransom note with an email address, and demanded $200 for the digital keys to unlock the files, the AP reports. Antivirus firm Symantec said Tuesday the problem was serious but not a high-level threat because it was widespread. The FBI said the scheme was unique, and leading security and antivirus firms this week are updating the software that companies and consumers use to defend against such attacks. Experts have dubbed the virus ''ransom-ware.'' The ransom was probably deliberately low to encourage payment and avoid law-enforcement involvement.