More than decade ago during systematic search for alternative reading frame derived peptides encoded by influenza A virus recognized by CD8+ T cells, PB1-F2 protein was discovered serendipitously by Chen et al. (2001). Since that time, an increasing body of evidence has continued to highlight the multifunctional meaning of this unusual influenza A protein. After twelve years of intensive research with 56 pubmed records for PB1-F2 in the title there is still a lot yet to explore. Is it a proapoptotic "explosive" protein that suppresses the mechanisms of early innate immune response or does it function as an NS1 antagonist? What is the root of its strain and cell specificity? What is the relationship between PB1-F2 and pathogenicity or secondary bacterial infection? Here we attempt to "take a trip" from the whole protein level through domains and regions to very particular aminoacid residues in correlation with its function in different virus isolates, cell type or animal model.