If you leave your antivirus software down--or even if you didn't left it--it is very hard to tell that your computer is not infected by viruses. If you have left your software running and your computer is infected, then you must be shocked or you think of changing the software or any other thing.
If you have this problem? You must need to keep your software up to date if not then your pc wii get infected, you will loose yous data, and even your pc can get crashed. And in last you unknowingly curse your software but in fact that happened because of your carelessness.
I should not say that every system failure is due to virus or worms or trojans. If your system is slowing, hardisk filling rapidly, programs crashing. This can be due to your operating systems or badly written programs which have many security vulnerabilities rather than viruses.
Do not open any suspicious emails and other things while surfing the net which can make you virusfree.
If any tools like gpedit.msc, taskmanager, regedit won't run in your computer then your pc can be infected.
You can find many things which indicate that your pc is infected. If you are not using your internet and still there is a a lot of network activity it is a very good proof that you have been infected. You can have a good firewall which will ask you before letting anything leave your pc. Windows firewall lacks in this capacity.
You can also use windows task manager which shows various processes running in your computer. If you find any process suspicious just close it or use google to find what is it. You can also find it in services.msc which shows every services running in your computer.
You can change the programs which loads in startup. If you reduce the number of programs in start up your pc will load faster then with those and if those are viruses they will not load.
Once you are sure that your computer is infected don't bother. There are some steps which can minimize the damage depending the level of protection.
I will say “Shame on you” if you do not have antivirus program. If your using linux distribution i can't say that cause there are very less no of viruses as compared to windows. If you have antivirus software and if it had stopped working then update it while surfing net or have free online scan from different websites.
Have a good firewall and antivirus software. If you don't want to waste money on these then go for AVG free antivirus. And be sure that your antivirus software is up to date.
