Adware:Adware (or spyware) is a small program that is designed to show advertisements (in various form and degrees of intrusiveness) on your computer. It often reports personal information back to its owners. As a result your sense of privacy can be violated.
SystemChecker is a rogue utility that may silently install itself by Trojans, through browser security exploits, or via other nefarious mechanisms. Once installed on your PC, SystemChecker will tease you with false notifications or alerts claiming that there are "critical files" in your version of Windows that may lead to data loss. SystemChecker will then attempt to trick you into buying an inferior data backup program. SystemChecker is known to be distributed through several malicious Trojans.
Technical details (How to remove SystemChecker(pop up))