Answers
Spreads without needing a host program
Users install it themselves without realising
Encrypts the files on a computer
Access restored after paying a ransom
Deletes, corrupts or modifies files
Needs a host program to spread
Spreads through shared infected files
Locks access to a computer
Holds the computer hostage
Replicates its code in other programs
Disguised as something the user wants
Gives hackers access to the computer
Overloads the network it spreads through
Backups allow recovery without paying
Replicates itself to spread
Might cause no damage
Hidden inside a useful program
Slows down networks and computers