A good one would not have allowed the virus to be loaded. A good one would get rid of it if it was there when you installed the antivirus program.
As far as your anti-virus program, I'm not that thrilled with SE. I have been using and recommending Norton Internet Security and it's predicessor for years. Even with all it's faults, it is the best one around. If you brought the machine to my shop, the first thing I would do is to load and run that.Sirefef.w or Win64/Sirefef.W is part of the ZeroAccess infection. Due to the Win64/Sirefef.W capacity of using random .dll file names to disguise itself and the possibility of been present in multiple iterations, the detection of Win64/Sirefef.W can be notably hard without an anti-malware program. Therefore, I don't recommend manual removal because removing the wrong file you can damage your hard drive and crash your PC. Find a good anti-malware tool capable of handling a rootkit infection to remove Sirefef.w from your computer safely. You can find all details about this threat at sirefef.w.