The best way to tell if your computer has a virus is by seeing if it has slowed down significantly in a short time. All computers slow down over time but if you notice your computer is suddenly running slow you may be infected.
You can use a virus identification tool. You should be careful and choose one from a reputable online company. Some virus are hidden within programs promising to spot viruses. Install an anti-virus program and have it run a test on your whole system.
If you suddenly see multiple pop ups on your screen for no reason your computer is certainly infected. Check your task manager when there are no programs loaded. Your CPU should be barely registering any cycles when no programs are loaded. If your Task manager is riddled with CPU cycles for no reason you should be suspicious.
Finally check to see if your Windows Machine still has the important Msconfig file. You also want to click on the start button then choose run and type in regedit to make sure that the registry still loads. If the Msconfig file is missing or the registry editor does not load you definitely have a virus.
