Thanks for all the valid points given. I will print the lot out for my future use.
I had to go to Jakarta yesterday, and bought a genuine copy of Kapersky AV2010. Here in Bali an original would cost treble and take a week of more to arrive.
First jobs last night were to wipe AVG and Malwarebytes. First reason was to avoid program conflict. I really appreciate those companies supplying a free program but in my particular case AVG missed the interlopers and Malwarebytes told me they were there but could do nothing about it.
Kapersky found the Trojans as Trojan-Downloader.Win32VB.aza no doubt other companies have their own name for it. There was an odd one 'PDM. Worm(dot)P2P(dot)generic' in 'ADOBEPIF' but I suppose it got planted there as the worm/trojan became active. My dots to avoid the invalid hash message.
Hopefully this is the end of the problem. Certainly as well as paying attention to all the advice given I will be checking every file on every disk and flash stick I have.
Thank you one and all. Tomorrow back to the swamps of PNG.