Q: After installing yosemite last night. My computer now acts like it has a virus. I can't get online without being attacked by adds and pop-up tabs of claims that I have a virus. Didn't have this problem before. Whats going on? I have already set my securit

You likely installed adware that is redirecting you to scam sites that have a JavaScript ransom stack embedded.

Stop pop-up ads and adware in Safari - Apple Support

Or simpler, http://www.adwaremedic.com/index.php

Your problem is most likely not caused by a "virus." It's a Web scam that only affects your browser, and only temporarily. There are several ways to recover.

1. If you're running Safari 8.0.7 or later and you see a dialog with the message “Don’t show more alerts from this webpage,” check the box and click OK.

2. If no other tabs or windows are open, or if you don't mind losing those tabs or windows, force quit Safari. Relaunch it by holding down the shift key and clicking its icon in the Dock.

The following steps may enable you to keep the state of other open tabs and windows.

3. Press the key combination command-W to close the tab or window. A huge box will pop up. Press the return key and both the box and the page will close. If that doesn't happen, continue.

4. Press and hold command-W. You may hear repeating alert sounds. While holding the keys, click the OK button in the popup. A different popup may appear, which you can cancel out of as usual.

5. From the Safari menu bar, select

          Safari ▹ Preferences... ▹ Security

and uncheck the box marked Enable JavaScript. If the Preferences menu item is grayed out, go to Step 2.

After closing the malicious page, select from the menu bar

          Safari ▹ Preferences... ▹ Privacy ▹ Remove All Website Data

to get rid of any cookies or other data left by the server. Open your Downloads folder and delete anything you don't recognize.

Hey Linc Davis, Im trying to post you a question but i don't know where. What happens it's that everytime I open safari, avast start popping lots of viruses and the URL of the safari even appear. I read a post from you that Avast suck and you linked a link of how to uninstall it but when i try to open that link on google chrome it comes and error "No data received ERR_EMPTY_RESPONSE", and this problem its not only with that link also with every link of my university every link that is .itesm doesn't open and it's the URL here. The curious thing is that i can open .itesm links on my house but not on the WiFi from here.

You may have inadvertently installed adware. You do not need to download or install anything to fix it.

For a description of how this may have occurred, how to avoid it in the future, and for Apple's recommended actions read How to install adware. Apple's instructions are linked in the Recovery Procedure near the end of that document. Read and follow them carefully. Pay particular attention to the easily overlooked passages directing you to restart your Mac when required.

Review your Gatekeeper settings: OS X : About Gatekeeper - Apple Support. Gatekeeper is designed to help prevent you from inadvertently installing garbage software.