Mark was using the same password for every site he went to. Leo said that he used to do the same thing. The importance of password security has snuck up on us, and we should all really be using a password vault like LastPass or 1Password. The main important difference between LastPass and 1Password is that LastPass keeps your vault on their servers, whereas 1Password gives you control over where the vault is stored. Each are very securely encrypted. But because LastPass keeps the vault on their servers, if Mark's password to LastPass is compromised, then all of his passwords can be stolen. Depending on how he manages his vault with 1Password, it could be more or less vulnerable than LastPass's solution.
No matter what Mark chooses, any password vault is a significant improvement in security than not using one.