Don't ognore it it will cmpromise your PC's security
Don't waste your time with products that offer to remove trojans etc from your PC often as a pop up aka scareware
Most antivirus programs will remove these pop ups by removing the malware that causes them - so will many anti spyware programs
I recommend Avast Anti virus along with Spybot S&D, A squared, and even Windows defender - all free. Use in conjunction with a secure browser like Mozilla Firefox (which is more secure by far than Internet Explorer ans stops most pop ups - in fact I've never had one for nearly 4 years since using Firefox) and a decent firewall like Comodo Firewall Pro (still free) and you're a way down the road to making and keeping your PC clean