Random Numbers Based On Points

I have this situation:

each user has some amount of points, for example:

table:users
user_id --- user_name --- points
1 --- user1 --- 100
2 --- user2 --- 100
3 --- user3 --- 100
4 --- user4 --- 200
5 --- user5 --- 500
-------------------
total points: 1000

I want to generate random selection of user, according to their points respectively, so the more points he has, the more likely he will be selected:

user1 in 10% cases
user2 in 10% cases
user3 in 10% cases
user4 in 20% cases
user5 in 50% cases

this percentage is respective to their points; I put some rounded numbers in the example - so total points of 1000 equals 100% - but they can have any amount of points: 1, 200, 3672 etc.