There has been a great deal of confusion over the recent Heartbleed bug.
Security experts have said it is not yet clear whether the scanning efforts are benign or are the work of cyber thieves keen to steal data.
Security professionals and developers previously advised people to change all their passwords; however Google said logins for its services don't need to be changed unless they were used on other sites.
Google contradicted other advice from Yahoo's blogging platform Tumblr, who told users they should change their passwords everywhere.
The conflicting guidance is further complicated with experts telling users that updating passwords is useless unless a website has patched its servers - but it is not always obvious to the public when this has happened.
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