In a detailed spatially explicit simulation study (Czárán & Hoekstra, 2009) we have shown that quorum sensing (QS)--the ability of bacteria to detect the local density of their clonemates in their immediate neighbourhood--might have evolved in synergism with cooperative behavior, i.e., the production of "public goods" like virulence factors for the common benefit of the cooperators, in spite of the fact that both cooperation and QS communication can be cheated (exploited) by mutant strains. In particular, we found that 1) cooperation requires an effective kin selection mechanism to operate, which is automatically supplied by the limited mobility of bacteria; 2) QS communication extends the scope for cooperation considerably, and cooperation maintains the selective advantage of QS communication, even if 3) different types of cheaters are always present and coexistent with "honest" phenotypes in a quasi-equilibrium. These predictions are validated by experimental results and field data by now, and medical applications of the results have been suggested.