The newest Netsky worm, which first appeared earlier this week, gathered steam on Thursday and caused security firms to upgrade their alerts to users.

Dubbed Netsky.ag by most anti-virus vendors, the worm remains concentrated in Brazil and Argentina, where it first appeared Wednesday, but copies have escaped South America to end up on machines around the globe.

The worm is relatively easy to spot by English speakers, since the subject headings used by this mass mailer are written in Brazilian Portuguese. Among the headings spotted are ones such as "Abra rapido isso!!!!" (open this now!) and "receitas de bolo" (cake recipes).

Netsky.ag spreads by sending itself to e-mail addresses it harvests from compromised machines, as well as through shared network folders and peer-to-peer networks.

If the attached file -- which comes in .pif, .com, .scr, .bat, or .zip -- is run, a dialog box pops up with text reading, "File corrupted replace this!"

McAfee raised its warning for Netsky.ag Thursday from Low to Medium because of a higher-than-usual number of copies submitted by customers and trapped by its e-mail snares.