For newly received Ark BTC, the user also faces the risk that the previous owner and the Ark service provider could collude to double spend it, which is similar to Spark BTC. The user can refresh the received Ark BTC to eliminate this counterparty risk, which Spark cannot do.
After refreshing, the counterparty risk for the Ark BTC is: *“if the user stays offline for too long (approximately one month) and their VTXO expires, the service provider may be able to take control of it.”*