Probably not a virus or trojan because they would have to be running for them to work.
But look up Rootkits, example explanation here; http://searchmidmarketsecurity.techtarget.com/definition/rootkit
Many anti-virus and anti-malware scanners can now find rootkits, but they change often and they are often difficult to find without special software, eg Sysinternals Rootkit Revealer.
Tell us what anti-virus you are running, and what other anti-malware scanners you are using.
is there a Trojan virus/ spyware already written/ developed that can uninstall itself whenever the hacker decides to?
so it will definitely be not detected by any antivirus / antispyware once it senses that the victim is now installing an antivirus/ anti- spyware?
for example, the virus/ spyware is controlled remotely by a hacker and its intention is to spy over me and then the hacker uninstalled it remotely so that i will not discover what happened?
because I'm really worrying whether there was indeed a spyware that was used against me in the past
but i just can not detect it now with my antivirus/ anti spyware (Microsoft Security Essentials) because the hacker or the intruder uninstalled it before i had the antivirus/ anti spyware?
thank you very much.
I really hope that this question will be answered.