While downloading Xplite, something came riding piggyback and made my WinXp unstable. Some porno program took control over my Control Panel and started running a blue film. I used Avast, Adaware etc. but of no avail, till someone suggested “ewido security suite”, which detected and removed 12 trojans+virus+malaware+cookies. I can understand about malaware+cookies but Avast leaving out trojans like “Qhost” is unexplicable. Now my system is good but is Avast still dependable?

It is not likely that XPLite caused the malware. Very likely something else was responsible for it.

QHost takes advantage of a “object type” vulnerability in Microsoft’s Internet Explorer browser. Exploits were discovered in september/october 2003. (more info)

1] There is no application, nor will there ever be, that can detect and remove all malware.

2] Avast’s main priority is detecting viruses, not all malware.

3]

which detected and removed 12 trojans+virus+malaware+cookies

trojans and viruses are malware.

Perhaps the definations HERE will help you to understand the differences.