It is very unlikely to be a vulnerability. However, to be honest, it's pointless telling us that someone "did something" to you that wasn't a backdoor - without details, it cannot be fixed, and pasting an action that they typed is not really a detail.
Unless you can obtain information from them about
exactly what they did and how they did it, we've got nothing to go on, nor has Khaled.
Nevertheless, I suggest you scan yourself for trojans - a lot of resources can be found in
this thread. Make sure you use more than one/two, as no ONE virus/trojan scanner can detect everything.
Regards,