Getting hash of a list of strings regardless of order

I would like to write a function GetHashCodeOfList() which returns a hash-code of a list of strings regardless of order. Given 2 lists with the same strings should return the same hash-code.

ArrayList list1 = new ArrayList()    
list1.Add("String1");
list1.Add("String2");
list1.Add("String3");    

ArrayList list2 = new ArrayList()    
list2.Add("String3");    
list2.Add("String2"); 
list2.Add("String1");

GetHashCodeOfList(list1) = GetHashCodeOfList(list2) //this should be equal.

I had a few thoughts:

1. I can first sort the list, then combine the sorted list into 1 long string and then call GetHashCode(). However sorting is a slow operation.

2. I can get the hash of each individual string (by calling string.GetHashCode()) in the list, then multiplying all hashes and calling Mod UInt32.MaxValue. For example: "String1".GetHashCode() * "String2".GetHashCode * … MOD UInt32.MaxValue. But this results in a number overflow.

Does anyone have any thoughts?

Thanks in advance for your help.