Trouble at the boutique

Yesterday I noticed that my computer was running slow and my security was working overtime removing trojans, the fact that it was removing them meant I didn't give it much more thought. Last night however,, it reached the point of audio ads playing in the background even when the browser wasn't open *MAJOR ALERT* but my security believed the computer to be clean and secure. Time to search the web for answers, I found a site that had a comprehensive removal of this problem using multiple cleaning apps, it took all night, the ads at one point actually seemed to be taunting me like children in a playground, sort of 'you can't catch me!' but guess what? I DID catch them and my computer is back to its old speedy self again. Have you ever had this problem? Did you clear it yourself or hand it to a pro to deal with? Samantha