Unix software should continue to grow in popularity despite negative publicity generated by a "virus" that brought thousands of Unix computers across the country to a halt last week, com-putermakers and users said.

The outbreak, the worst of its kind to date, came at a time when computer companies were having increasing success in selling Unix-based systems to commercial customers.Unix, an operating system that controls the basic functions of a computer, has been used mostly in the academic world. But aggressive marketing to businesses by vendors such as American Telephone & Telegraph Co., Hewlett-Packard Co. and Sun Microsystems Inc. has made Unix one of the hottest-selling segments of the computer market.

The virus, apparently planted by a Cornell University graduate student, highlighted the vulnerability of Unix to security breaches. In just one day the rogue program spread to some 6,000 computers connected through the Internet network.

But computer makers and users said that steps were already being taken to fortify Unix against viruses and other security dangers, making it unlikely this attack would make corporate customers abandon plans to buy Unix.

And by calling attention to the security issue, the incident will likely speed the development of more sophisticated anti-viral techniques, they said.

"Ultimately, this could have a positive effect by making people more sensitive to security problems," said Bill Klinger, Unix product manager for AT&T, which developed Unix in the 1960s.

Any operating system is susceptible to a virus, a program that is placed secretly into a computer and then spreads to others by phone lines or software discs.

Unix has tended to be more vulnerable than others because its biggest users are willing to sacrifice security in order to promote an environment where they can experiment with and write new programs for Unix. Moreover, the computers on which Unix is most often found are linked by a variety of communications networks that allow for the free flow of information - and viruses.