Nonetheless, spyware remains a costly problem. When a large number of pieces of spyware have infected a Windows computer, the only way to get rid of them may involve backing up user data, and fully reinstalling the operating system. For instance, some versions of Vundo cannot be completely removed by Microsoft, PC Tools, Symantec and others because it infects Internet Explorer, and Windows' lsass.exe (Local Security Authority Subsystem Service) with a randomly-filenamed dynamic link library (or dll). These can be very helpful.