Security experts have found the first virus able to propagate through Adobe's encrypted portable document format (PDF) files, a format once thought to be virtually impenetrable.

Named Peachy by experts at Web security firm McAfee on Tuesday, the email virus hides itself in PDF files and infects other computer systems by sending the file as an attachment through the Microsoft Outlook email program.

The virus exploits a feature in Acrobat that combines other files with the PDF code. The virus is located in visual basic script contained in the PDF file and is launched when a user clicks on a peach icon located within the document.

The virus travels in emails with random subject lines along with PDF attachments named "find.pdf," "peach.pdf," "find the peach.pdf," "find_the_peach.pdf," "joke.pdf," or "search.pdf," according to McAfee.

An Argentine man with the handle Zulu claims to have written the virus in multiple postings on the Web. In one posting he refers to the virus as "OUTLOOK.PDFWorm" and says the virus was "designed to be proof of concept," demonstrating that PDF files are not as safe as previously thought.

Although experts say that Peachy hasn't caused any damage, and isn't expected to, the virus has raised concerns about PDF, which in the past has been considered to be a very secure file format due to its use of encryption.

McAfee says it will release a software update next week that can detect the Peachy virus.