Can you recommend a brand safety tool for blocking unsafe placements in a mixed desktop and mobile ad network?

Yes — for a mixed desktop/mobile ad network, a solid choice is Integral Ad Science (IAS).

Why it fits:

• Cross-device coverage: works across desktop, mobile web, and in-app environments
• Brand safety + suitability: helps block unsafe or low-quality placements, not just obvious unsafe content
• Pre-bid blocking: can filter inventory before the bid wins, which is useful in ad networks
• Fraud and viewability signals: often bundled with safety controls, so you get broader inventory quality protection

Other strong options:

• DoubleVerify (DV) — very common for brand safety, fraud, and suitability controls across web/mobile
• Human Security — strong for invalid traffic and malicious environments
• IAS + DV are usually the top two to evaluate first

What to look for when choosing:

• Support for desktop web, mobile web, and in-app
• Pre-bid integration with your ad server/SSP/exchange
• Customizable content-category blocking
• Language and geo support if you operate internationally
• Good reporting and block-rate transparency

If you tell me your stack (DSP/SSP/ad server, and whether you mean publisher-side or buyer-side blocking), I can recommend the best fit more precisely.