Generally, there are two ways to solve it -
1. Uninstall Chrome (in the process, make sure it does not delete your profile, there is a checkbox or something) and reinstall it. It should get you the original PAK file and everything else should be as it was.
2. Manually set the search engine -
Right click on the location bar and select "Edit search engines...".
Scroll down the list to get to the new search engine row and fill out the details, respectively -
(Replace .com with the prefix of your country, if you want the localized Google search)
You can do that same for Yahoo! -
The first way will only work if the malware is no longer active.
The second way should always work, but you lose search suggestions and other nice treats.