NEW YORK (AP) _ A ''worm'' that sends an anti-nuclear message has invaded at least 50 computers in a worldwide scientific network, security officials said.

The worm, software similar to a computer virus, is annoying but relatively harmless, said Ron Tencati, security manager for the Space Physics Analysis Network in Greenbelt, Md.

It flashes a message saying: ''Worms Against Nuclear Killers

''Your System Has Been Officially WANKed.''

The network, with more than 15,000 computers, links many universities and government installations such as the National Aeronautics and Space Administration and Defense Department research centers. None of the computers on it is involved in top-secret work, Tencati said Tuesday.

The worm, first spotted early Monday, can get into computers only when their users have neglected fairly basic security procedures, Tencati said. Security at most computer centers is good enough that the worm should not spread too widely, he said.

On Friday, a rare but harmful virus known as Datacrime or Columbus Day was triggered in some personal computers around the world. The less-destructive ''worm'' found this week affected larger computers.

Besides flashing its anti-nuclear message, the worm frightens computer users by making them think incorrectly that their files have been deleted. It also scrambles passwords and flashes short messages - including some racial and ethnic slurs - to other, uninfected computers.

The Wank worm has not caused damage at any NASA installation - especially the Kennedy Space Center, which planned today to launch the shuttle Atlantis - according to Charles Redmond, a NASA spokesman.

''No secret data, no classified data, nothing of a national security nature has been violated,'' Redmond said.

The worm attacks a network of Digital Equipment Corp.'s Vax computers known as DECnet Internet. That network is similar to but separate from the main Internet network, which was attacked last year by a worm created by a Cornell University graduate student.

The main components of the DECnet Internet are the NASA-administered Space Physics Analysis Network, with about 5,500 computers, and its European counterpart, the European Space Physics Analysis Network, with about 500; as well as the High Energy Physics Network, with about 8,000 computers, and its European counterpart, European HEPnet, with about 1,000.