A government-led task force is warning companies doing business over the Internet to tighten security after an increase in computer attacks that have focused on systems related to E-commerce or banking and financial businesses.

In its advisory, the National Infrastructure Protection Center cites three holes in Microsoft Windows NT that are increasingly used by intruders to gain unauthorized access to computer systems and download proprietary information. The center is urging systems administrators to apply patches that will close the holes.

The center has also warned against new holiday-oriented viruses, such as "Navidad," a Spanish-language E-mail worm, and "Music," an E-mail attachment that displays a picture of Santa Claus and plays several seconds of "We Wish You a Merry Christmas" while it sends itself to all the recipients in the infected user's address book.

The center was established in 1998 as a joint effort between the FBI, various federal and state government agencies, and the private sector. Its mission, according to its Web site, is to "serve as the U.S. government's focal point for threat assessment, warning, investigation, and response for threats or attacks against our critical infrastructures."