Google is redesigning Chrome malware detections to include password-protected executable files that users can upload for deep scanning, a change the browser maker says will allow it to detect more malicious threats.

Google has long allowed users to switch on the Enhanced Mode of its Safe Browsing, a Chrome feature that warns users when they’re downloading a file that’s believed to be unsafe, either because of suspicious characteristics or because it’s in a list of known malware. With Enhanced Mode turned on, Google will prompt users to upload suspicious files that aren’t allowed or blocked by its detection engine. Under the new changes, Google will prompt these users to provide any password needed to open the file.

Beware of password-protected archives

In a post published Wednesday, Jasika Bawa, Lily Chen, and Daniel Rubery of the Chrome Security team wrote:

Not all deep scans can be conducted automatically. A current trend in cookie theft malware distribution is packaging malicious software in an encrypted archive—a .zip, .7z, or .rar file, protected by a password—which hides file contents from Safe Browsing and other antivirus detection scans. In order to combat this evasion technique, we have introduced two protection mechanisms depending on the mode of Safe Browsing selected by the user in Chrome.

Attackers often make the passwords to encrypted archives available in places like the page from which the file was downloaded, or in the download file name. For Enhanced Protection users, downloads of suspicious encrypted archives will now prompt the user to enter the file’s password and send it along with the file to Safe Browsing so that the file can be opened and a deep scan may be performed. Uploaded files and file passwords are deleted a short time after they’re scanned, and all collected data is only used by Safe Browsing to provide better download protections.

For those who use Standard Protection mode which is the default in Chrome, we still wanted to be able to provide some level of protection. In Standard Protection mode, downloading a suspicious encrypted archive will also trigger a prompt to enter the file’s password, but in this case, both the file and the password stay on the local device and only the metadata of the archive contents are checked with Safe Browsing. As such, in this mode, users are still protected as long as Safe Browsing had previously seen and categorized the malware.

Sending Google an executable casually downloaded from a site advertising a screensaver or media player is likely to generate little if any hesitancy. For more sensitive files such as a password-protected work archive, however, there is likely to be more pushback. Despite the assurances the file and password will be deleted promptly, things sometimes go wrong and aren’t discovered for months or years, if at all. People using Chrome with Enhanced Mode turned on should exercise caution.

A second change Google is making to Safe Browsing is a two-tiered notification system when users are downloading files. They are:

1. Suspicious files, meaning those Google’s file-vetting engine have given a lower-confidence verdict, with unknown risk of user harm
2. Dangerous files, or those with a high confidence verdict that they pose a high risk of user harm

The new tiers are highlighted by iconography, color, and text in an attempt to make it easier for users to easily distinguish between the differing levels of risk. “Overall, these improvements in clarity and consistency have resulted in significant changes in user behavior, including fewer warnings bypassed, warnings heeded more quickly, and all in all, better protection from malicious downloads,” the Google authors wrote.

Previously, Safe Browsing notifications looked like this:

Over the past year, Chrome hasn’t budged on its continued support of third-party cookies, a decision that allows companies large and small to track users of that browser as they navigate from website to website to website. Google’s alternative to tracking cookies, known as the Privacy Sandbox, has also received low marks from privacy advocates because it tracks user interests based on their browser usage.

That said, Chrome has long been a leader in introducing protections, such as a security sandbox that cordons off risky code so it can’t mingle with sensitive data and operating system functions. Those who stick with Chrome should at a minimum keep Standard Mode Safe Browsing on. Users with the experience required to judiciously choose which files to send to Google should consider turning on Enhanced Mode.