"Smart" viruses such as this one will re-create it's files, folders, registry entries, and processes with multiple layers of redundancy. There will be a process that prevents opening the task manager to avoid getting halted. Another will re-generate deleted files. A on-boot executable will do this also. A heavily buried registry entry will direct a second, backup copy to re-infect in case anything is missing. Deliberate breaches in browser security and settings will be introduced to leave the system vulnerable to re-infection.
The exact extent varies, but if you can just delete a file and be done you either deleted a file left intentionally to attract your attention, or just a weak infection.