How to respond: Many viruses can be contained or removed with antivirus software. The Gpcode.ak virus is an exception. However, Kaspersky Lab, which sells antivirus programs, recently released a free program, StopGpcode, that may help you unlock your files without capitulating to the blackmailers.

Preventive measures: Install antivirus software on all company computers and keep the virus definitions up to date. And make sure to back up your data frequently, just in case you need to revert to the last system-restore point before the virus hit. You can also use services like Postini, which, for about $12 per user per year, will remove viruses from e-mails before they reach your inbox. Companies of a certain size can try something called application whitelisting. Programs like Bit9's Parity, which is available for about $30 per computer for a minimum of 100 machines, allow only software approved by the IT department to run on employee computers.