So far I've found two culprits, though there may also be a third. Both are dealt with in the same way, so the instructions to fix the problem apply to either.
- Site Advisor (McAfee)
These Chrome extensions are causing the internal broken links by adding undefined to the URL. The latter may or may not be clashing with AVG Safe Search, if the user has both added.
These are not malware, nor are they loaded with spyware. Your system is quite safe and secure.
Complitly is advertized as a search engine tool. It guesses what you're searching for and so completes the URL. It could be viewed as useful for those who struggle with spelling, as the search term does not have to be exact.
McAfee is a reputable antivirus software. It blocks malicious programs and the like from infecting your computer. Site Advisor is just one component in the whole package. It inspects the webpage before it loads, then sends an alert if all is not well.
The 'undefined' error does not occur within the remit of either of these tools. It's merely a glitch that somehow got into their usual programming, when coupled with the Chrome browser. It's probably just coincidental that the former is a rival to Google, while the latter has been purportedly rendered obsolete by the in-built security programs in locked-down Chromebook.
I'm so glad I use Firefox.