Yesterday is a simple COM file infector. Every 128th time the virus is run it adjusts the computer's date backwards by one day.
The virus contains the texts '[pepper]' and 'yesterday once more'.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
More information on 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.