To connect GT-I9300 phone you have to perform the following steps:
1. Disconnect USB cable from phone.
2. Go to Menu->Settings->Developer options.
3. Turn on "USB Debugging" option.
4. When message is appear press "Yes".
5. Connect usb cable to phone.
6. Go to dial window.
7. Enter *#9090# number.
8. Set speed to 115200.
9. Reboot phone.
10. Press "Read Info" in software.
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Platform: Samsung Android
Selected port: COM4
Selected model: GT-I9300
Please, press "OK" button on the phone to allow USB debugging..
Proper android device not found. Make shure that "USB debug" option on the device is turned on.
Write IMEI failed
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Platform: Samsung Android
Selected port: COM4
Selected model: GT-I9300
Please, press "OK" button on the phone to allow USB debugging..
Detected phone model: GT-I9300
Firmware compiled date: Fri Dec 27 20:07:47 KST 2013
PDA version: I9300XWUGML4
CSC version: I9300ODDGML4
SW version: I9300DDUGMK1
Phone IMEI: 004999010640000
Phone SN: 00000000000
Android version: 4.3 (JSS15J)
Checking Root:
Phone is Rooted.
Reading security backup, please wait...
Backup saved as C:\Program Files\Octoplus\Octoplus_Samsung\BACKUP\Security-GT-I9300-Unknown22-11-2014_14-05-53-.asec file
Cheking security type...
New security type is detected
Old IMEI: 004999-01-064000-0
New IMEI: 353922-05-********
Repairing IMEI ...
Executing exploit...
Exploit has been executed successfully
Repairing network. Please wait, this can take some time...
Network is successfully repaired
Phone will restart now
IMEI successfully repaired.
To finish the operation, please restart the phone via phone's menu (don't disconnect the battery!)