If you notice several symptoms, however, you may have a virus. Programs take longer than normal to load into the computer. There is more disk drive activity. For example, disk drives run longer when doing a simple directory. Error messages occur regularly that previously did not exist.
Less memory is available than usual.
The executable size of programs has changed. There is a sudden reduction in the amount of available disk space. Programs or files mysteriously disappear. Unexplained hidden files are present. A disk is no longer bootable which was in the past.