Sure we can. Biological life is something that replicates autonomously using DNA contained inside the apparatus of at least one cell. Viruses are not alive because they can not replicate on their own and do not produce their own cells. More abstractly life is something that follows the Darwinian program as demonstrated on Earth. If you had competing, replicating programs in a virtualised Earth-like environment I would say they were alive too if they could fully reproduce and establish resource economising ecosystems on their own.