MADISON, Wis. (AP) -- The Wisconsin Better Business Bureau is urging consumers to be skeptical of e-mails that look like they're from legitimate shipping companies.

The agency says a new string of phishing e-mails is making the rounds this holiday season.

Phishing is an online scam where hackers create valid-looking e-mails, usually to trick recipients into revealing private information.

The bureau warns of recent phishing e-mails that appear to come from shippers including FedEx, UPS and Wal-Mart.

The subject line suggests there was a problem with a delivery and the recipient should open an attachment for further instructions. The attachment contains a computer virus.

Other false e-mails look like surveys or e-cards.