Spyware and Adware can also direct you to "chosen" sites when using an internet browser, which can be very annoying as most times they have nothing in common with the sites you really want. They download unwanted cookies and they can appear to hijack your homepage and any other favourite sites.
They are generally more of a pest than Virus' and Trojans as these are dealt with by your Anti-Virus software without any trouble at all.
If you have been surfing the net for some time without anti spyware you will be amazed at the amount of spyware that Ad-Aware and Spybot can turn up, remember to update them before first use and regularly, and also it's good advice to run both of them because anything one of them misses will be found by the other.
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