Ability to interfere the system code is about Trojans. Somehow they intervene : via active code, via mail or via maleware. The Flashget application was downloaded from the site, installed and used 2-3 times for downlloading torrents, after this the windows code was down and the systems failed. The antivirus software Avast would easily determeine the virus related application, but after the complete installation the Trojan remained active and stopped the windows startup, after this the registry analysing showed it was still active.