I was glad that I switched to Avast anti-virus software from Grisoft. Last night, I found four trojans while I was scanning some data on an old HDD which previously had Grisoft Anti-Virus software installed on it. I found that despite constant updates and scanning, Grisoft had often failed to detect viruses and trojans. It was the second or third time this had happened.
The funny thing was that I wasn't a bittorrent user either. The last time I had downloaded anything was at least four years ago.