"System Security" rogue anti spyware program

[DFH]

A friend of mine has this nasty on his computer. He's running XP Home. His antivirus, Symantec CE, has been disabled along with his firewall. I'm unable to install SAS or MalwareBytes (or anything else on his box). Safe mode does not load, SAS's RUNSAS.EXE does not run, taskmanager does not run and system restore does not run. Apparently no executable will run. Symptoms are numerous popups, fake virus alerts, fake virus scans, etc, ad nauseum! I ran Avira's boot disk on his box and it detected a number of trojans including mirar(?) and others but did not delete any of them. I'm going to try Bitdefender's boot disk tomorrow but if anyone has any suggestions...I'd sure like to hear them.

[DFH]

UPDATE: I ran Bitdefender from a boot disk and that cleaned the box enough for me to get into SAFE mode. From there I ran SAS's RUNSAS.EXE which further cleaned up enough to let me download and install MalwareBytes. Between those two programs in Normal and Safe mode, plus Avira, Autoruns, Windows Defender and CCleaner, my friend's computer is about 99%. This "System Security" rogue program is a tough nut.