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'.
Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.
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See the manual for your F-Secure product on the Help Center.
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