Z-90 activates in July and December if an infected file is executed and the time is exactly 09:03. At this time the virus encrypts the DOS boot sector of drive C:, making the PC unbootable (encryption is done by XORing with 16-bit hex value 0903). After this it displays this message:
VIRUS Z-90. JUNIO 95. M EXICOSE MURIO TU DISCO DUROTU LO PUEDES RE VIVIRHAS BAILADO ALGUNA VEZ CON TU NOVIA A LE TENUE LUZ DE LA
Z-90 was found in the wild in Brazil in April 1996.
Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.
More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.
You may also refer to the Knowledge Base on the F-Secure Community site for more information.