They are neat technology, but it is bad if they make people think it is generally safe to reuse them. It is not. If you use them, you should make a new silent payment address for every service you use, and if it an anonymous service (like a swap service) you should make a new one for each *payment.*

Otherwise you are subject to two attacks:

1. Profiling

A supposedly anonymous service, like a swap service, can create a hidden profile of a user based on the address they send money to. E.g. if I use it twice with the same silent payment address, they can keep a record of that and know that at time A I received $20 and at time B I received $35, because I reused the same silent payment address. Thus they create a hidden profile on me and learn *when* I use their service and *how much* I swap there day to day, which is info they should not know. Mitigating this attack requires creating a new silent payment address for each payment whenever you use an anonymous service like that.

2. The colluding sender attack

This attack also relies on address reuse. In it, two people -- Alice and Bob -- observe that Alice sent $10 to the same silent payment address that Bob sent $5 to. So together they know the same person received at least $15, which they should not know. Ideally, Alice should only know about *her* payment and Bob should only know about *his.* But if I reuse the same address, they can compare notes and learn that both of their payments went to the same person. That's a privacy leak, and to mitigate it, you must not give the same silent payment address to two different people. Make a different one for each such payment.