… is a bad thing. Some think they can strengthen their defences against malicious code by installing multiple anti-malware applications.
This is plain wrong: Having more than one anti-malware software on a single computer will lead to unpredictable problems, such as false positives, false negatives and other system errors.
You should pick one of the few mainstream anti-malware solutions and stick to it. All of them are good enough for most users, some are more user friendly than others. The free ones are also reliable these days. The most important thing to remember though, is that there is no such thing as 100% protection on any operating system or platform. Most of today’s malware take advantage of users not being responsible about their browsing/e-mailing habits.
Help your choice of anti-malware software keep your computer clean by thinking about what you click on!