As said on the link you point to, this vulnerability concerns only pre-2003 versions of Microsoft LSASS. It also says that some worms are known to try and exploit this vulnerability to propagate. Essentially, they just try and send a request to your OS's Local Security Authority Directory Service (whatever that is, it's probably built-in many Windows versions because used to build corporate networks). If the worm is lucky, you will be running a LSA DS, and if even more lucky it will be old enough for the exploit to work and for the worm to gain control of that service and do whatever wormy things it needs to do.
So, you're not very concerned so far. Your OS is recent enough for this vulnerability to have been fixed and no worms or viruses can exploit it.
But this is not the end of the story. You stated that this happened when you plugged in your mobile 3G stick. Hence it's very likely that your 3G stick executes some code when plugged (either via an exploit in a Windows driver, or because you installed some software that allows it to, or because that very component is expected by Windows to run some code when plugged; I'm not a Windows user so I have no idea), and that this code contains at least one exploit. It is quite likely that it also contains other exploits, to increase the chances of taking over your machine. Maybe some of these other exploits work on Windows 7.
You should first assess the reputation of the 3G key provider and manufacturer. Have they been caught serving malware to their clients before? Or are they themselves potentially victims of an employee or outsider? Do you trust them? It's up to you to decide that but I would contact them and ask why their 3G key seems to be containing malware. If I were you, I would run a full scan of my system with whatever antivirus utility I can put my hands on. It's not impossible that you're infected by some other exploit.