An email computer virus that comes concealed as a Net movie hit several U.S.-based companies Friday afternoon, leading at least one antivirus company to upgrade its threat assessment from "medium" to "high" risk.

An email computer virus that comes concealed as a Net movie hit several U.S.-based companies Friday afternoon, leading at least one antivirus company to upgrade its threat assessment from "medium" to "high" risk. The virus, dubbed "Creative," carries no destructive payload, but automatically emails itself to a victim's entire email address book. It was first identified in Europe on Thursday, where it had been spreading slowly. But the worm began picking up steam in the United States by late Friday, according to McAfee's Anti-Virus Emergency Response Team (AVERT). Even though the virus does not carry a destructive payload, it can crash email servers if it gathers enough steam, Vincent Gullotto, AVERT's senior director, warned, noting that much of the damage caused by the infamous "I Love You" virus was caused this way. He added, however, that the spread of the virus could be blunted over the weekend, when fewer employees have access to their work computers. "Creative" comes in an email with the header "A great Shockwave flash movie," referring to a popular Internet animation format. It has several aliases, including Prolin, Shockwave, W32/Prolin@mm, TROJ_SHOCKWAVE and TROJ_PROLIN. Prolin is short for "Pro-LINUX," so-called because the virus inserts harmless messages on victim computers plugging the open-source operating system. Like numerous other recent viruses, Creative targets Microsoft's Outlook and Outlook Express email clients and spreads by sending itself to everyone in a victim's email address book. It also adds itself to the Windows operating system start-up menu.