Microsoft Corp. on Monday issued an emergency security warning saying that hackers have found a way to booby-trap certain common Word files with the .rtf extension.

The only way to be sure your computer won't get infected is not to open a document with the .rtf file extension until Microsoft says it's fine to do so.

This is the worst kind of attack. A hacker who manages to get you to open a booby-trapped file can gain control of your computer. From there, the hacker can do all kinds of things. For instance, the hacker can turn your computer into a so-called zombie by putting it on an illegal botnet. That means hackers can use your computer as part of a bigger network of computers to do all kinds of illegal things — like send spam, spread viruses, and commit fraud.