If your modem has this problem, this means anyone on the Internet can send a ping packet to your system containing "+ + + ATH0" that your system will echo back through your modem, causing your modem to hang up.
Since most modem control software no longer uses the escape sequence to control the modem, one fix for this problem is to disable it. Adrian Gonzalez pointed out that the problem itself can be used to apply the fix: by sending a ping with "+ + + ATS2=255&WO1", vulnerable modems can be made to drop to command mode, disable the escape code, save the setting permanently, and then return to online mode. The command to accomplish this is:
ping -c 1 -p 2b2b2b415453323d32353526574f310d
If you press the button below, this page will send you just such a ping, provided you are not viewing this page through a proxy. Note: this may result in your net connection being terminated, as the O1 part of the command may be ignored. If you are disconnected, try this page a second time - if the fix took effect then you should not be disconnected a second time.