A method of maintaining an Instant Message IM session, comprising: receiving at a first login server a login request associated with a client, wherein the login request includes client account information and a client security key; establishing the IM session and transferring Instant Messages between the client and the first login server, wherein establishing the IM session includes: verifying, by the first login server, the login request; and if the verification is successful, storing, by the first login server, a first set of property information of the client, wherein the first set of property information comprises the client account information and a server security key generated by the first login server according to the client security key; and sending, by the first login server, and indicator indicating that verification is successful to the client, wherein the indicator comprises the server security key; detecting an interruption in the transfer of the Instant Messages; sending to the client an address of a second login server by a login allocation server; receiving at the second login server a reconnection request from the client, wherein the client sends a reconnection request using the received address of the second login server and wherein the reconnection request includes a second set of property information comprising the server security key generated by the first login server; and in the event that the reconnection request is accepted by the second login server, exchanging Instant Messages between the client and the second login server. receiving at a first login server a login request associated with a client, wherein the login request includes client account information and a client security key; establishing the IM session and transferring Instant Messages between the client and the first login server, wherein establishing the IM session includes: verifying, by the first login server, the login request; and if the verification is successful, storing, by the first login server, a first set of property information of the client, wherein the first set of property information comprises the client account information and a server security key generated by the first login server according to the client security key; and verifying, by the first login server, the login request; and if the verification is successful, storing, by the first login server, a first set of property information of the client, wherein the first set of property information comprises the client account information and a server security key generated by the first login server according to the client security key; and sending, by the first login server, and indicator indicating that verification is successful to the client, wherein the indicator comprises the server security key; detecting an interruption in the transfer of the Instant Messages; sending to the client an address of a second login server by a login allocation server; receiving at the second login server a reconnection request from the client, wherein the client sends a reconnection request using the received address of the second login server and wherein the reconnection request includes a second set of property information comprising the server security key generated by the first login server; and in the event that the reconnection request is accepted by the second login server, exchanging Instant Messages between the client and the second login server.