After a quiet holiday away from PC viruses, users returning to work Wednesday were warned by anti-virus vendor Symantec Corp. about the slowly spreading Maldal.D worm.

The worm, also known by its subject line, “ZaCker,” has the ability to delete data, including system files and anti-virus files that haven’t been updated to detect it, according to Symantec. The worm spreads by mailing itself to users through Microsoft Corp.’s Outlook e-mail program, according to information on Symantec’s Web site. Symantec discovered the worm on Dec. 29.

The content of messages that carry the worm ranges from “If you have an elegant taste” to “For everybody wants to marry a woman that he doesn’t love!” Symantec said. Once executed, the worm then deletes various files with suffixes including .INI, .EXE and .JPG.

Symantec has rated the damage potential of the virus as medium, while competing anti-virus vendor Corp. has rated it as low risk.

“We have not seen enough (instances of the virus) to upgrade it to medium risk,” said April Goostree, virus research manager for

Several worms that attack anti-virus software have appeared in recent months, so suggests customers use a firewall in combination with anti-virus software, Goostree said.

Another way to prevent the spread of the worm would be for customers to stop using Outlook, Goostree said. “It’s using Outlook and (Outlook) Express to propagate,” she said. “It doesn’t have the ability to send itself.”

Moreover, although using other e-mail applications, such as IBM Corp.’s Lotus Notes or Qualcomm Inc.’s Eudora, would not spread the worm to others, few see straying from Microsoft as an option.

“It’s not that practical to people,” Goostree said. “Everybody wants to use the same platform.”

Symantec Corp., based in Cupertino, Calif., can be reached at Corp., in Sunnyvale, Calif., can be contacted at