viruses, worms, similarities and differences

Whats  the similarities and differences between viruses and worms.

 After doing so, you need to perform some internet research on actual real world examples where organizations in any sector (retail, banking, healthcare, etc.) were impacted by either viruses or worms and what they did to defend against them. 

In addition, you need to explain what repercussion(s) the organization experienced, in terms of, publicity, financial impact, customer dealings and investments made to better protect all those impacted.