By today many services like twitter offer simple posting via SMS. Unfortunately this can be misused easily by using tools likesmstools Update: sendpage or yaps which allow to send sms via modem or ISDN. The problem with this tools is that the sender can be set to anything – including the victim’s mobile number. So anyone with the software and a modem who knows your MSISDN can post to your twitter account or blog and pretend to be you. This of cause is also valid for peer to peer SMS. I don’t understand why not even a simple 4 digit pin mechanism is implemented in this services to validate the user…