If you are still on Windows XP, it's time to get off! Support ends in a month. Microsoft will no longer provide security fixes for the aging OS. If you must run it, make sure you have an antivirus program (NOT Microsoft Security Essentials) and do NOT use Internet Explorer. Use Google Chrome or Mozilla Firefox.
You know you have to be careful when on the internet. You even have to be careful while using search engines. Be aware that the first few Google search results are advertisements and look at the URL before you click on a result.
To the left is an example of a recent top search result on Google for “iTunes.” Notice that it’s an advertisement and the URL that is referred to is not related to Apple.com. (This has been fixed, by the way). However, to click on this link takes you to a legitimate looking page to download iTunes. If you download iTunes here, the install puts all kinds of spyware on your computer. You can opt out of installing the "crapware" but most people don't notice.
This brings me to my second point which is no one pays attention when installing software to what actually gets installed.
Two major culprits in the problem of legitimate software installing junk are Adobe and Java. You get a notice to update Java and while it is updating, you click right through the screen to the left.
By not unchecking the box on this screen, you install the Ask Toolbar which is filled with ads and far less useful than Google or Bing as a search engine. I see this toolbar on almost every computer I service.
Adobe Reader and Flash updates come bundled with McAfee Security Scan Plus which is another unnecessary program that only tries to get you to buy McAfee antivirus. You must uncheck this box while installing the relentless Adobe updates. I also find this software on most computers.
Why do legitimate companies like Adobe and Java do this? Because they are getting paid by the writers of this crapware to add these installs to their downloads. A pox on their houses! Maybe someday, we can live without Adobe and Java and be done with this nefarious business practice.